
C 535 
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917 
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EXPERIMENTAL 
ELECTRICAL TESTING 



A COMPILATION, INCLUDING PRACTICAL ELECTRICAL 
MEASUREMENTS ACTUALLY PERFORMED BY STUDENTS 



We. 

MONOGRAPH B-4 

AUGUST, 1917 
SECOND EDITION 



ISSUED FOR 

SCIENCE TEACHERS IN EDUCATIONAL INSTITUTIONS 



"Everybody needs to know something about the working of electrical 
machinery, optical instruments, ships, automobiles, and all those labor- 
saving devices, such as vacuum cleaners, tireless cookers, pressure cookers 
and electric irons, which are found in many American homes. We have, 
therefore, drawn as much of our illustrative material as possible from the 
common devices in modern life. We see no reason why this should detract 
m the least from the educational value of the study of physics, for one can 
learn to think straight just as well by thinking about an electrical generator, 
as by thinking about a Geissler tube." 

From "Practical Physics." Black & Davis. 



WESTON ELECTRICAL INSTRUMENT CO. 

NEWARK, N. J. 



Mouosrraph 



Copyright, 1914, 

BY 

WESTON ELECTRICAL INSTRUMENT CO. 



.NfcS3 



W 1 

£<?(>V CONTENTS 



SUBJECTS 

PAGE 

Argument 5 

General Laboratory Work 7 

Resistance Measurements 11 

A Complex Lamp Bank 13 

Testing Fuses 17 

Induction 22 

The Photometer 28 

Incandescent Lamp Testing 32 

Electroplating 34 

The Use of the Electric Heater in Efficiency Tests 38 

The Electrolytic Current Rectifier 53 

The Weston Direct-current Movable-Coil System 65 

The Weston Alternating- and Direct-current "Movable-Iron" System. . 68 

Co-operators 70 

An Appeal 78 

EXPERIMENTS 

1. Resistance of a Conductor by the Substitution Method 11 

2. Comparative Resistance of Various Conductors 13 

3. Constructing and Testing a Lamp Bank Rheostat 13 

4. Test of Fuses 17 

5. The Fusing Effect of an Electric Current 19 

6. Currents Induced by Magnetism 24 

7. Currents Induced by Electromagnetism 26 

8. An Exercise in Photometry 28 

9. Practical Incandescent Lamp Testing 32 

10. Electroplating with Copper 35 

11. The Electrochemical Equivalent of a Metal 36 

12. The Electric Disk Stove or Hot Plate 41 

13. Cost of Operating and Efficiency of an Electric Flatiron 43 

14. Boiling an Egg by Means of Electricity 47 

15. The Immersion Heater 48 

16. Making Cocoa and Candy with the Aid of Electricity 49 

17. Testing a Nodon Valve with Dry Cells 55 

18. Testing a Nodon Valve with a Direct-current Service Line 56 

19. Testing a Nodon Valve with Alternating Current 57 

20. Efficiency Test of a Nodon Valve 58 

21. Efficiency Test with Two Nodon Valves in Series 59 

22. Puncturing the Insulating Wall of a Nodon Valve 59 

23. Efficiency Test of a Commercial Electrolytic Rectifier 62 

3 



ARGUMENT 



THE Weston Monographs were prepared with the definite 
object in view of attempting to co-operate with and 
assist science teachers in high schools and collegiate 
preparatory schools throughout this country. 

Their context is exclusively on electrical subjects; and each 
deals with a particular theme. 

For instance, B-l dwells upon the manifest advantages of 
training students engaged in laboratory work by means of stand- 
ard apparatus, such as they will encounter in practical work 
after graduation. It also calls attention to the fact that it is 
inconsistent as well as unwise to attempt to perform modern pro- 
gressive laboratory work by means of antiquated and obsolete 
apparatus. It shows what should be done. 

B-2 contains a series of simple yet exceedingly instructive 
experiments, and presents suggestions that should be of great 
value in the preparation or amplification of an electrical course. 
It tells what could be done. 

B-3 briefly describes several standard high grade and 
thoroughly reliable instruments, economical in price and par- 
ticularly adaptable to high-school work. 

In this Monograph B-4, we have compiled interesting and 
important data which will indicate some of the experiments 
which are actually being performed in progressive High Schools 
in these United States. We accomplished this by reproducing 
the actual work of students without revision or alteration, 
together with sketches, data-sheets, reports and instructors' 
comments, as well as apparatus actually used. 

We desire to explain as briefly as possible how B-4 has been 
produced. 

Early in the Fall of 1913, we issued a letter to over 7000 
science teachers on our list, in which we directed attention to 
the Monographs we had already issued, and requested sugges- 

5 



6 ARGUMENT 

tions relating to experiments in electrical measurements which 
they would like to see embodied in future Monographs. "We 
were immediately deluged with replies, and as soon as it was 
feasible we began preparing data relating to the experiments 
most in demand. 

We then conceived the idea of asking science teachers to 
furnish us with these experiments, instead of preparing them 
ourselves; and wrote to a number of those who were fortunate 
enough to possess a modern equipment, inviting them to con- 
tribute some specified exercises. 

In this manner we hoped to fulfill the requests of science 
teachers by publishing the work of other science teachers. 

The experiments offered are reproduced verbatim; but we 
have in some instances either simplified or elaborated connec- 
tion diagrams. Otherwise the authority for the execution of 
the work is vested in the contributor cited. Necessarily there 
was much repetition, and it obviously became practicable to 
print only a few of the contributions we received; but we desire 
to gratefully acknowledge the assistance of those teachers whose 
work is not incorporated in this Monograph. Their tests were 
of great value to us and in many cases it was exceedingly difficult 
to make a choice- 

Entirely aside from their intrinsic pedagogical value, the 
majority of these experiments have a significance which cannot 
fail to arrest the attention of the progressive instructor. They 
prove conclusively that the trend of physics teaching is toward 
the practical application of fundamental principles. 

They indicate also that laboratory work requiring the use 
of instruments of precision may be successfully performed by 
young students of either sex. 

In conclusion we desire to direct special attention to the 
Xodon Valve and Rectifier experiments; because they are not 
only of the greatest interest pedagogically, but since they also 
possess utilitarian properties, in that they indicate how a teacher 
who has only alternating-current service available, may easily 
and cheaply transform to direct current; and thereby open up a 
greater realm of electrical experiments specially suited to the High 
School Laboratory. 

Weston Electrical Instrument Company. 



GENERAL LABORATORY WORK 



In preparing the minds of beginners in experimental electrical 
work, and in directing their attention to the ethical as well as 
the material considerations involved, it would be to their advan- 
tage to hear the following comments, which are adapted from 
an introduction to a loose leaf manual in Electrical Measure- 
ments. We are indebted to their author, Prof. James Theron 
Rood, Ph.D., of Lafayette College, for permission to use them. 

I. PREPARATION FOR LABORATORY WORK 

A well-trained experimenter, in any department of science, 
may at once be known by his ability to make clear, concise state- 
ments of the laws and phenomena of that department in which 
he is especially interested. 

An electrical laboratory is a place designed to help men to 
acquire such characteristics, but it is of value to any man only 
in proportion as he approaches his work therein with the proper 
spirit, imbued with the desire to do and learn. The first requis- 
ite is to come to the laboratory knowing fully what you are to 
do, and how you are to do it. Read in advance the direction 
sheets for the given experiments, look up the references, be 
prepared to get the most out of your performance of the given 
experiment. If you do not come so prepared, you are almost 
sure to become confused as to what must be done and as to the 
order which must be followed. Required observations are likely 
to be omitted, time may be wasted on useless readings, interest- 
ing and valuable phenomena may escape your attention or be 
wrongly interpreted, and you may finish with a confused instead 
of a clear conception of the method and the value of the test. 
Make yourself master of the experiment, in the preparation for 
it, in the performance of it, and in the writing of the report 

7 



8 GENERAL LABORATORY WORK 

about it. The students who must continually run to an instruc- 
tor for direction and advice can never rise very far. 

II. PERFORMING THE EXPERIMENT 

No general advice or directions can be given which will cover 
each and every experiment. Each test brings its own peculiar- 
ities, its own difficulties; but there are invariably certain things 
which mark the trained and careful experimenter. Some of these 
are given in what follows: 

III. APPARATUS 

All apparatus used in testing should be most carefully han- 
dled. What company would retain an employee who misused 
its instruments or machines? 

Accidents may happen to even the most careful experiment- 
ers, but whenever they do occur, they should be reported at 
once. Placing the injured instrument back in its place without 
reporting its injury is the work of a sneak. Such action may 
result in the apparatus remaining unrepaired until a time when 
a co-worker, needing the apparatus for immediate use, discovers 
that it is injured and that it may have to be sent away for 
repairs. He is thus kept back in his work when, had the injury 
been known, suitable repairs might have been made before the 
apparatus was again needed. 

IV. DIAGRAMS 

Before beginning any experiment, make a clear diagram 
of the proper arrangement of all circuits to be used, with all 
connections, instruments, resistors, switches, cut-outs, etc., 
shown by the conventional symbols. Use heavy lines for 
indicating conductors carrying large currents, such as elec- 
tric power service wires, bus-bars, feeders for motors, etc., 
and light lines for potential circuits, such as leads to the 
e.m.f. terminals of wattmeters, voltmeters, etc. Submit this 
diagram to the instructor for his criticism and approval. Then 
connect up according to this diagram. Make no changes in it 
without the approval of the teacher. 



GENERAL LABORATORY WORK 



V. INSTRUMENTS 

Almost without exception all makes of ammeters have un- 
insulated, metal binding-posts, while voltmeters have posts 
encased in insulation. The two kinds of meters can thus be 
at once told apart. Millivoltmeters are frequently used as 
ammeters by connecting shunts in the line, the potential drop 
across these shunts being proportional to the current; the read- 
ings of the meter when its leads are placed across the terminals 
of the shunt will be proportional to the current flowing, and 
may be read directly in amperes. When so used the values 
of the scale divisions of the meter will depend upon the partic- 
ular shunt used as well as upon the meter leads. Each milli- 
voltmeter must always be used both with its own shunt and its 
own leads. The shunt is always connected in the line and the 
millivoltmeter across the shunt. Remember, ammeters go in 
the line, voltmeters go across the line. Never lay instruments 
on the floor or on a chair. Always put them on a table and 
then pass the wires through holes in the edge of the table or else 
so fasten them that there can be no chance of an instrument 
being pulled down onto the floor. If any instrument has a zero 
error reading, allow for it in your readings, or have it reset by 
means of its zero adjusting device. Never open or close a 
circuit at any ammeter binding post. Trace out the polarity 
of any D.C. circuit before connecting in an instrument. Be 
sure that the current flows through the instrument in the right 
direction. If it does not, open the circuit before reversing 

ANY AMMETER LEADS. REVERSE VOLTMETER LEADS AT THE CIR- 
CUIT end, not at the meter. Read all meters to one-tenth 
of the smallest division. Look for any parallax when making a 
reading. 

VI. ORDERLINESS 

During the performance of all tests, see that all instruments, 
switches, lines, etc., are kept in an orderly condition and not 
allowed to become a confused maze. After finishing an experi- 
ment, see that all instruments, rheostats, lamps and other pieces 
of apparatus are replaced in their proper places in their cases. 

Coil up and put away all lengths of wire. Put everything 



10 GENERAL LABORATORY WORK 

back in its place and leave the apparatus as well as all the tables, 
etc., free from all wires and in perfect order ready for the next 
users. When finished replace covers on all motors or dynamos 
used. Next to success in the performance, orderliness in the 
handling of laboratory apparatus is the most important thing 
to be learned in a laboratory. Your care in this respect will be 
considered in determining your term grade. 

VII. REPORTS 

To be able to write a satisfactory report of an investigation 
is an art and accomplishment that should be the desire and pride 
of every engineer, in every walk of science. It is the keystone 
of all science. In its essence, an engineer's report is a why, 
a what, a how, a this and a therefore. 

A good engineer must have knowledge, judgment and common 
sense. The laboratory, rightly used, is the best place for the 
development of such powers, and should be valued as such. 

Let your laboratory motto be: , 

WORK— OBSERVE— THINK 



EXPERIMENTAL ELECTRICAL TESTING 



EXPERIMENT NO. 1 
RESISTANCE MEASUREMENTS 

The following experiments were selected from a number 
kindly contributed by Mr. William F. Evans, Instructor in 
Physics, Girls' High School, Brooklyn, N. Y. 

They are copied from the laboratory note-book of the girl 
who did the work. 

A modification of these methods is used in shop practice 
for a preliminary measurement of resistance wires in course 
of manufacture. To eliminate errors due to a variation in cur- 
rent, the wire and the rheostat are both connected with one 
pole of the cell, and a double-throw switch is used, so that the 
rheostat may be adjusted until the same deflection is obtained 
when current is passed through either circuit in rapid succession. 
Reference, "Laboratory Exercises," Fuller and Brownlee, page 
270. 

Resistance of a Conductor by the Substitution Method 

Apparatus. Weston ammeter; dry cell; rheostat; 50 cm., 
No. 30 German silver wire; and leads. 

(1) Connect up the cell, the ammeter and the unknown 
resistance in series, being sure that all contacts are clean and all 
connections tight. See Fig. 1. 

(2) Substitute the resistance box (with all plugs removed) 
for the unknown resistance and then decrease the resistance 
of the circuit until the current is the same as before. See 
Fig. 2. 

(3) W T hat then is the resistance of the 50 cm. No. 30 G. S. 
wire? 

11 



12 



EXPERIMENTAL ELECTRICAL TESTING 



Student's Report 

(1) I connected up as in diagram the cell, the ammeter, 
and the unknown resistance (50 cm. No. 30 German silver wire) , 




Fig. 1. — Resistance Measurements. (Reproduced from Student's Sketch.) 

Evans' Method. 
Instrument Used is a Model 280, Weston Ammeter. Range 15 Amperes. 

being sure that all contacts were clean and all connections tight. 
The indicated current was 6 amperes. 

(2) I substituted the resistance box for the unknown resist- 
ance with all plugs out, and reduced the resistance of the cir- 




D. C.AM METER 




CZZlf 




Fig. 2. — Resistance Measurements. (Reproduced from Student's Sketch.) 

Evans' Method. 
Instrument Used is a Model 280, Weston Ammeter. Range 5 Amperes. 



cuit by putting in plugs until the reading of the ammeter was 
the same as before. Resistance was 1.8 ohms. 



COMPARATIVE RESISTANCES OF CONDUCTORS 13 

(3) The resistance then of 50 cm. of No. 30 G. S. wire is 
1.8 ohms, because the reading was the same when the resist- 
ance box was connected as when the German silver wire was 
connected. 

EXPERIMENT NO. 2 

COMPARATIVE RESISTANCES OF CONDUCTORS 

Apparatus. As in preceding experiment; together with other 
wires of various sizes. 

OBSERVATIONS 





Length of Conduc tor 


Area of 

Cross-section. 


Amp. 


Ohms. 


(1) 

Varying Lengths . . 


(1) 50 em. G. S. wire 

(2) 100 cm. G. S. wire 

(3) 150 cm. G. S. wire 


.05 sq.mm. 
. 05 sq.mm. 
.05 sq.mm. 


.60 
.32 
.20 


1.8 
3.4 
5.6 


(2) 
Varying Areas 


(1) 50cm.G. S.wire 

(2) 50 cm. G. S.wire 

(3) 50 cm. G. S. wire 


.05 sq.mm. 
. 10 sq.mm. 
.15 sq.mm. 


.60 
1.04 
1.34 


1.8 
.8 
.5 


(3) 
Varying material. . 


(1) 50 cm. G. S.wire 

(2) 50 cm. brass wire 

(3) 50 cm. copper wire 


.05 sq.mm. 
.05 sq.mm. 
.05 sq.mm. 


.65 
2.28 
3.70 


1.9 
.3 
.1 



Description. I connected up the German silver wire as in 
preceding experiment. Then I substituted the resistance box 
as in preceding experiment. First I used 50 cm., then 100, 
last 150 cm. of German silver wire. Next I used wire with 
.05 sq. mm. cross section; then 10 sq. mm., finally, 15 sq. mm. 
After this I used 50 cm. of brass and 50 cm. of copper wire in 
place of the German silver wire. 
March 21, 1913. 



EXPERIMENT NO. 3 

CONSTRUCTING AND TESTING A LAMP BANK 
RHEOSTAT 

In commercial work, adjustable rheostats are extensively 
used; in fact, they are indispensable when current from service 
lines is employed for experimental purposes. 



14 



EXPERIMENTAL ELECTRICAL TESTING 



For precision tests in laboratories, rheostats that are non- 
inductive and which have a negligible temperature coefficient 
are preferable and often necessary, but in general commercial 
testing adjustable lamp bank rheostats are most in demand for 
current regulation, or for building up a load. 

The rheostat described in this experiment should appeal 
to the science teacher because it is simple in construction and 
yet permits a wide range of adjustment owing to the ingenuity 
of its designer. 

This rheostat was designed by Charles P. Rockwell, and 
constructed by him with the assistance of Gordon R. Milne, 
Barringer High School students, Newark, N. J. The tests 
made with it are their joint work. 




Fig. 3. — A Complex Lamp Bank. 

Following is their own description: 

This board was designed to allow any number of lamps, 
up to twelve, to be connected in multiple, series, or multiple 
series. 

An oak board was obtained from the school shop. Accord- 
ing to plan, a Perkins 25 amp. double-pole single-throw switch 
and a fuse block were placed at the extreme right, four Perkins 
single throw, single-pole switches were placed next to these, two 
for ingoing and two for returning current. Two other Perkins 
switches placed next allowed current to cross over to different 
banks of lamps. Twelve sockets were screwed at equal dis- 
tances from each other. 



TESTING A LAMP BANK RHEOSTAT 



15 



The small cut-out switches were made by bending copper 
strips into jaws for receiving copper strips as blades. Holes 
were bored to receive jaws which were sealed in place with seal- 
ing wax. 

Connections were made and lamps were screwed in as shown 
in Fig. 3. 

Apparatus and Materials Required 



195 
WATTS 



rOO 

-oo 
-oo- 

-oo 



258 
WATTS 



1 Weston voltmeter. 

1 Weston ammeter. 

1 portable testing set. 

1 oak board 18X40 ins. 

1 Perkins knife switch, 
25 amp., double pole, single 
throw. 

6 Perkins knife switches, 
25 amp., single pole, single 
throw. 

Sheet copper for mak- 
ing 27 switches (jaws and 
blades) which may be replaced with Trumbull single-pole, 
single-throw switches. 

1 Edison double-plug cut-out. 

12 Bryant porcelain receptacles, keyless. 

12 carbon filament 32 

rOOOn 

-ooo- 




Fig. 4. 



122 

WATTS 



-ooo 
ooo 




30 
WATTS 



>WATTS 



Fig. 5. 

IV, V, VI, VII, VIII. 
T, U, V, W, X. 



C.P. lamps. 

2 fuses, mica cap, 15 
amp. 

15 ft. No. 14 (B. & S. 
gauge) bare copper wire. 
Directions for Oper- 
ating and Testing 

Note. All switches 
not specified closed must 
be open. For all lamps 
in multiple: Close III, 
C, D, E, F, G, H, K, L, M, N, 0, P, S, 



16 



EXPERIMENTAL ELECTRICAL TESTING 



For all lamps in series. Close III. VI. IX. A. F, I K 

Q. v. y. it;, p. g. 

For Multiple Series Grouting 

Three groups in series, each group containing four lamps 
in multiple. Close all except IV. V, VII. VIII. LX 

Two groups in series, each group containing four lamp ; 
multiple. Close all except III. V. VII. VIII. IX. 



CKXX> 

K-:-:-> 



*TTS 



Fig. 6. 

arrangement 



Mflitipk 



No. of 



Multiple Series. SeeF:; 4 



>::.-= :: 



Xo. in Mult. 



Watta 



124 
248 



12S 

60 
17 

27 



2 in series 
2 in series 



2 in mult. 

3 in mult. 



WATTS PER LAMP IN ABOVE ORDER 1st COLUMN 



12S 
195 
256 



0&O 

695 


o 
6 


15 


Multiple Seeiz b Bee Rg 




-4 r 


7 


- " 


3 in series 


_ ... znuit. 


80 


955 


8 


10 


3 in series 


3 in mult. 


122 


1080 
1197 
1310 


9 
10 
11 


8 


3 in series 


4 in mult. 




Multiple Sbkks 




1420 


12 


5 


4 in series 


2 in mult. 


■" 








4 in series 


2 in mult. 


60 








4 in series 


3 in mult. 


85 



Lamp N 


1 


2 




4 


5 





7 


8 


9 


10 1 


:: 


Watt= 


124 


124 


120 


120 


100 


::: 


: "■: 




'- v ~ 


us : 


i:: 



TEST OF FUSES 



17 









RESISTANCE PER 


LAMP 










Lamp No. . 




1 


2 


3 


4 


5 


6 


7 


8 


9 


10 


11 


12 


Res 


Hot 


112 


112.2 


116 


116 


139.2 


126.3 


124.2 


126.3 


118.8 


118.0 


123.2 


126.3 


Res 


Cold 


225 


230 


240 


230 


235 


235 


230 


245 


225 


242 


235 


240 



R (hot) was when filaments were incandescent. 

V 2 118 2 

Formula used R= — or R= . 

W W 

R (cold) was when lamps were at room temperature (22° 
C). Results were obtained by measurement with a portable 
testing set. 

EXPERIMENT NO. 4 

TEST OF FUSES 

From Lafayette College, Department of Electrical Engineering, Labora- 
tory Direction Sheets. Available through the courtesy of the author, 
Professor J. T. Rood. 

References: Barr, Direct Cur. Elec. Eng., p. 479; Swenson and Franken- 
field, Vol. I, p. 342; Standard Handbook for Elec. Engs., p. 585; Foster's 
Handbook, pp. 217, 1275. 

Purpose. Every electric circuit should be provided with 
some form of apparatus designed to prevent the flow of any 
excessive current which might start a fire or burn out any appa- 
ratus. The insurance companies require that all lighting and 
motor circuits shall be so fused or protected that the current- 
carrying wire shall never be overheated. Such protective devices 
are called cut-outs. They may be put into two classes, fuses and 
circuit-breakers. Fuses, according to their arrangement, may 
be divided into three classes, open, expulsion and enclosed. 
Circuit-breakers are somewhat more convenient, but are much 
more costly and occupy more space. They are better for cir- 
cuits carrying large current, or where the circuit is liable to be 
opened or overloaded frequently, since they are more sure of 
opening the circuit. 

Construction. Fuses are merely strips of metal of such 
shape and material as will fuse or "blow" before any excess 
current can flow for any length of time. The I. R. losses in the 
metal due to the current passing causes the strip to become 



18 EXPERIMENTAL ELECTRICAL TESTING 

heated. If the heat is generated faster than it can be radiated, 
the fuse material melts and the circuit is thus opened, provided 
the arc does not hold between the terminals of the fuse block 
on account of the metallic vapor which may be left in the air 
between them. This limits the amount of current which a 
given fuse can safely break, unless there is provided some means 
of expelling the hot vapor (expulsion fuses), or of condensing 
it (enclosed fuses). In this last the vapor is supposed to be 
immediately condensed in the spaces between the granules of 
the non-inflammable, non-conducting material which fill the 
tubes. On account of the variation of the alloy in the different 
parts of the fuse wire, as well as on account of the effect of air 
currents, open fuses cannot be depended upon to always blow 
at the same current with the same length and diameter of fuse 
wire. For open fuses alloys of lead, antimony and bismuth 
.are mostly used. Enclosed fuses are mostly of zinc. For large 
fuses copper is sometimes used, but it is liable to hold the arc 
through its vapor. 

Object. The object of this experiment is to test some com- 
mercial fuse wire and to determine the relation (a) between 
length and the fusing current, (b) between diameters for this 
last, (all diameters of wires tested should be of the same make) , 
(c) to investigate the construction and action of some types of 
•enclosed fuses. 

Apparatus. Various diameters of fuse wires, fuse block 
with adjustable terminals, adjustable resistor, Weston ammeter 
and inch scale, also line switch. 

Part I. Set the terminals of the fuse block 1% inches apart 
in the clear and insert a length of fuse wire. Connect the 
fuse block in series with the ammeter, adjustable resistor and 
switch; and connect the whole across the D.C. supply circuit. 
See that the resistance is set to allow only a small current to 
flow, close the switch and slowly increase the current until the 
fuse blows. Repeat with the same size of wire for fuse lengths 
of 2, 2%, 3, and 3% inches. Repeat this series for all the dif- 
ferent diameters of wire given you. Record make of wire, rated 
capacity, and blowing current. Calculate and record the per- 
centage ratio between the rated capacity and the blowing cur- 
rent. Note carefully the construction of each fuse. 



THE FUSING EFFECT OF AN ELECTRIC CURRENT 19 

Report. Describe what you did. Plot curves showing (a) 
relation between length and fusing current for wires tested, 
(6) relation between diameter and fusing current for a given 
length of fuse. The form of curve for this last is usually: 

*=(//a)*, 

where d=diameter of wire; 
1= fusing current, and 

a=constant depending on the composition of the wire. 
Give good sketches of the construction of the enclosed fuses 
tested and give description of the details of each. 

Questions, (a) Do you think the size or mass of the ter- 
minals of the fuse block can affect the value of the fusing current? 

(b) If so, how? 

(c) Would this effect be proportional for all lengths of the 

fuse wire? Why? 

(d) Why should the current in every case be increased slowly? 

(e) Why should the enclosed fuses be given a preliminary 

heating before being blown? 

EXPERIMENT NO. 5 
THE FUSING EFFECT OF AN ELECTRIC CURRENT 

The following experiment on fuses was supplied by Mr. 
Milton M. Flanders of the Bliss Electrical School, Takoma 
Park, Washington, D. C. It is so clean-cut and practical that 
comments are superfluous. Sketch is a reproduction of the one 
sent in by the students performing the test. 

TEST NO. A-400 

Heat 

A study of the fusing effect of an electrical current. 

Object of Test 

To determine the current and time required to melt fuses 
under various conditions. 



20 



EXPERIMENTAL ELECTRICAL TESTING 



Apparatus Required 



1 ammeter (0-100) 
1 rheostat 
1 stop watch 
1 thermometer 



Various fuses 
1 circuit breaker 
1 switch 
Connecting wires 



Conduct of Test 
I. Preparation. Set up the apparatus as per diagram, con- 
necting to a source of low potential and high current, as a stor- 



CIRCOIT BREAKER 




AMMETER 



Fig. 7. — Study of the Fusing Effect of an Electrical Current. 
(Reproduced from Students' Sketch.) Flanders' Method. 

Instrument Used was a Model 1, Weston Ammeter. Range 100 Amperes. 

Note. — For all ordinary laboratory work, fuses that will "blow" at 1 
to 20 amperes will suffice, and an ammeter of lower range than the above 
will be preferable. 

age battery. Close switch S and after inspection by instructor, 
admit current and correct polarity of ammeter if necessary. 
See Fig. 7. 

II. Operation, (a) Admit current to 200 per cent rating 
of fuse under test, holding this constant by means of the rheo- 
stat R. Open switch $ and simultaneously start stop-watch. 
Note the exact time required for the fuse to open the circuit. 
Repeat at least three times. 

(6) Repeat above with different fuses, as directed. 

(c) Repeat above on increasing current, the rate of increase 
being 1 ampere per minute, and tabulate results. 



THE FUSING EFFECT OF AN ELECTRIC CURRENT 21 

(d) Repeat operation (a) with the fuse wire in contact with 
some foreign insulating substance. 

(e) Repeat operation (a), first raising temperature of fuse 
50° C, by means of a heating chamber. 

III. Calculation. Tabulate all results as indicated below: 



Fuse. 


Wire. 


Length. 


Deg. C. 


Rating 


Amps. 


Time. 


Note. 


Link 


Shawmut 


1.625 


17.8 


6 


12 


10 

11 

11 

Avg. 10.66 + 





Report on Test No. A-400 



Instrument used: Weston Model 1, Ammeter No. 5378. Centigrade 
Thermometer No. 3. 

DATA 









Operation (a) 






Type. 


Wire. 


Length 
Ins. 


Temp. 
Deg. C. 


Rating 
Amps 


Amps. 


Time, Sec. 


Remarks. 


Daum 
Daum 
Daum 


Shawmut 
Shawmut 
Shawmut 


1.625 
1.625 
1.625 


22 
22 

22 


6 
6 
6 


12 
12 
12 


8.6 

7.2 

10.0 


Average 

Time 

8.93+ sec. 


Operation (b) 


Type. 


Wire. 


Length. 
Ins. 


Temp. 
Deg. C. 


Rating 
Amps. 


Amps. 


Time, Sec. 


Remarks. 


Link 
Link 
Link 


Shawmut 
Shawmut 
Shawmut 


1.625 
1.625 
1.625 


17.8 
17.8 
17.8 


6 
6 
6 


12 
12 

12 


10 

11 
11 


Average 

Time 

10.66+sec ; 


Operation (c) 


Type. 


Wire. 


Length. 
Ins. 


Temp. 
Deg. C. 


Rating 
Amps. 


Amps. 


Time, Sec. 


Remarks. 


Daum 
Daum 
Daum 


Shawmut 
Shawumt 
Shawumt 


1.625 
1.625 
1.625 


21 
21 

21 


6 
6 
6 


12 
10 
10 


12min. 
9min. 
9min. 


4 sec. 
20 sec. 

12 sec. 



22 



EXPERIMENTAL ELECTRICAL TESTING 

.7I7.ATION (d) 







I enn . 


r.iV- - 


Amps. 


See. 




Type. Wire. 


Amp 5 




T.inV | Shawmut 
link Shawniut 
link Shawmut 


1.625 

1.625 
1 -'. 


17 9 
17.8 


6 
6 

6 


12 
12 

12 


21 
19 

22 


Average 

Time 

20.66-^: 



Note. — In operation (d> the fuse wire was in contact with a marble 
block for .75 in. of its length. 









Operation 


(e) 






Type Wiis 




Temp. Rating 

I::."C A-rsT An;; 


1— e. 5*:. 


Remarks. 


T.inV 


Shawmut 
Shawmut 


1 . 625 
1.625 
1.625 


49 
49 

49 


6 
6 
6 


12 
12 
12 


8.2 

7.2 
8.0 


Average 

Time 
7 B sec. 



Note. — None of the above fuses would blow at rated current and 
normal temperature of surrounding air. 

Above test performed by F. G. Shipley and L. T. Pe::: 

Instrument repairs are expensive ! 

Fuses are cheap ! 

Why not insist that students insert a fuse between the 
load and the ammeter in all tests, so that the ammeter cannot 
be burned out or overloaded? — Compiler's Note. 



INDUCTION 

We requested Mr. Geo. M. Turner of the Department of 
;.nd Chemistry, Masten Park High School. Buffalo. 
N. Y.. to contribute some exercises on Induction, because the 
effects due to induction must often be taken into consideration 
in the designing or use of commercial apparatus in order to 
obtain efficient results. In this respect, the effect of induction 
may be beneficial or harmful but a knowledge of this phenome- 
non is always necessary before a student can make any progress 
in acquiring even an elementary knowledge of electrical measure- 
meL- 

Mr. Turner intends to include the following experiments 
in his physics course and writes concerning them as follows: 



INDUCTION 23 

"Your request for an experiment on Induction for the forth- 
coming Monograph received. 

"It is my understanding that you desire an experiment that 
will include the center-scale millivoltmeter. As my pupils have 
not as yet used this instrument for their induction work, it would 
be impossible to furnish any results from their standpoint. 

"Recently, I used the instrument in a series of induction 
tests, such as our high-school young people make, and found 
that while not as sensitive as the ordinary D'Arsonval Galvanom- 
eter used in high- school work it was sufficiently sensitive, for such 
experiments as our young people would need to do. The prompt 
return of the pointer to the zero reading and the ease of watch- 
ing the scale made the millivoltmeter seem much better adapted 
for this work than was the galvanometer. 

"Later I tried the millivoltmeter in connection with the- 
'Student-sliding- contact Wheatstone Bridge' of the wire type. 
With resistances about 10 ohms, the instrument was all that could 
be desired, admitting of the exact location of the contact to 
within a millimeter. With resistances about a hundred ohms 
the instrument gave a width to the neutral point of between 2 
and 3 millimeters. When the resistance was increased to 1000' 
to 4000 ohms, the neutral point was extended to approximately 
10 millimeters. By increasing the battery power for the higher 
resistances from 1 cell to 3 cells, the range of the neutral point 
was reduced to 2 or 3 millimeters (for the 4000 ohms). 

"These results indicate an amply sensitive instrument for 
such work in the hands of the high-school student, as his results 
need not vary as much as 1 per cent. It is very likely that many 
of the resistance boxes, used in the high-schools, will vary as 
much, or more than 1 per cent. Again, the prompt return of the 
pointer to zero reading proved of great assistance, and a marked 
time saver. 

"In general, I am very much pleased with the results of the 
working of the instrument. It is my intention to order enough 
for our laboratory work early next year. 

"Very sincerely, 

"(Signed) Geo. M. Turner. 

"It may be proper for me to advise you that the customary 
(high school) slide wire bridge uses one meter of wire." 



24 



EXPERIMENTAL ELECTRICAL TESTING 



EXPERIMENT NO. 6 

CURRENTS INDUCED BY MAGNETISM 
Object of Experiment 

(1) To observe the effect of moving a magnetic pole into a 
coil of wire. 

(2) To compare the effect of moving a magnetic pole into 
the coil with that of removing the pole from the coil. 

(3) To observe the effect of moving unlike poles into a coil. 

(4) To observe the effect of moving the coil instead of moving 
the magnet. 

(5) To observe whether the induced current aids or opposes 
the movement between the coil and the magnet. 




ZERO CENTER 
MODEL 280 



Fig. 8. — Current Induced by Magnetism. Turner's Method. 

Instrument Required is Model 280, Weston Zero Center Millivoltmeter. 
Range 100-0-100 Millivolts. 

Apparatus 

Weston millivoltmeter with zero in the center of the scale. 
Coil of wire (50 to 100 turns of No. 28 double-cotton covered 
wire) . 

Small bar magnet. 

Connecting wires. 

Procedure 



Preliminary. Before making the tests called for in this exper- 
iment it is desirable to find out the direction of thrust of the milli- 



CURRENTS INDUCED BY MAGNETISM 25 

voltmeter needle, when current enters it by the right-hand bind- 
ing post. In order to determine this, a thin strip of zinc may 
be fastened to one end of a connecting wire and the other end 
attached to the left-hand binding post of the millivoltmeter. 
With the second wire attached to the right-hand binding post, 
the zinc and copper ends of the wires may be dipped in ordinary 
hydrant water, or (if this has not enough conductivity) into 
hydrant water with a few minute crystals of salt added. 

The information gained by the thrust of the needle under 
these conditions serves as a guide to the direction of current 
flow through the millivoltmeter during the tests that follow. 
Of course, current entering the millivoltmeter by the left-hand 
binding post produces a thrust of the needle in a direction oppo- 
site to that caused by current entering by the right-hand bind- 
ing post. 

Connect the terminals of the coil to the millivoltmeter. 

Manipulation 
II 

(a) While watching the millivoltmeter, the North pole of 
the bar magnet may be thrust into the center of the coil and 
held there. The movement of the needle, during the movement 
of the magnet, to left or right is noted. See Fig. 8. 

(b) Upon removing the North pole, a movement of the 
needle in a direction opposite to that of the entering pole is 
observed. 

(c) To show that a temporary current through the milli- 
voltmeter is due to the relative motion between the coil and 
magnet, the coil may be moved toward and from the North pole 
of the magnet, with results similar to those observed under 
(a) and (b). 

(d) When the South pole, instead of the North pole is used, 
a second series of observations is obtainable, which gives move- 
ments of the needle opposite to those of (a), (b) and (c). 

(e) In order to show that the rate at which the lines of force 
(thrust out by the magnet) are cut by the wire of the coil, alters 
the deflection of the needle (and hence the electromotive force 
of the current produced) , the magnet may be made to enter the 
coil at first slowly, then more rapidly. 



26 EXPERIMENTAL ELECTRICAL TESTING 

(/) After a record has been made of the result of the observa- 
tions of (a), {b), (c) , (d), it is quite possible, by use of the pre- 
liminary information, bearing upon the movement of the milli- 
voltmeter needle when the current enters the right-hand binding 
post, to find out (by Ampere's hand rule) whether the polarity 
of the coil of wire is such as to produce a magnetic pole that helps 
or hinders the movement between the coil and magnet in each 
of the trials (a), (b) , (c), (d). 

EXPERIMENT NO. 7 
CURRENTS INDUCED BY ELECTROMAGNETISM 

Object of Experiment 

(1) To observe the effect in a coil of wire, of moving another 
coil of wire, through which a current is flowing, toward the 
former coil and away from this coil. 

(2) To observe the change of effect when the moving coil has 
a soft iron core. 

(3) To observe the effect in a coil of wire of "making" and 
"breaking" the current in an adjacent coil of wire. 

(4) To observe the change of effect when the two coils have 
a common soft iron core. 

(5) To observe whether the induced current aids or opposes 
the movement. 

Apparatus 

Weston millivoltmeter, with zero in the center of scale. 

2 coils of wire 50 to 100 turns each of No. 28 D. C. C. wire. 

2 dry cells. 

Soft iron core. 

Connecting wires. 

Procedure 

Connect up the apparatus as shown in the diagram, leaving 
the two coils apart. See Fig. 9. 

(a) With current flowing through the coil A, it should be 
moved toward the coil B until the two touch and have their 



CURRENTS INDUCED BY ELECTROMAGNETISM 27 

axes coincident. The direction of movement of the needle during 
the movement of the coil is noted. 

(b) After allowing the needle to come to rest, the two coils 
may be separated and the direction of movement of the needle 
during motion again noted. 

(c) By placing a soft iron core within the coil A and repeat- 
ing the movement to and from coil B, the change in the intensity 
of the thrust of the needle of the millivoltmeter and hence 
a change in the electromotive force in the circuit, is observable. 

(d) With coils A and B side by side (axes coincident), the 
current through coil A may be opened and closed by use of 
one of the wire ends at the battery. The direction, as well as 




ZERO CENTER 
MODEL 280 



Fig. 9. — Current Induced by Electromagnetism. Turner's Method. 

Instrument Required is Model 280, Weston Zero Center Millivoltmeter. 
Range 100-0-100 Millivolts. 



the intensity of the thrust of the needle should be noted, both 
on closing and on opening the circuit. The intensity may be 
still further varied by the introduction of the soft iron core into 
the coils. 

(e) While recalling the direction of thrust of the needle when 
current was made to enter the right-hand binding post of the 
millivoltmeter from the simple cell of the previous experiment, 
it is possible to trace out, by Ampere's hand rule for finding the 
polarity of a solenoid, whether the magnetic poles, formed by 
induction in B, assisted or hindered the movement of the mag- 
netic poles in A; or whether, on making and breaking the circuit 
in (d) the polarity of B and A was such as to hinder making 
contact and prolong the contact when made, or the reverse. 



28 EXPERIMENTAL ELECTRICAL TESTING 

We hoped to obtain additional exercises on induction from 
other sources, shoeing, for instance, the inductive effect of an 
electromagnet in shunt with a lamp and an instrument: so that 
students would have a clear conception of the commercial impor- 
tance of induction phenomena. See '"Practical Physics." Black 
and Davis, page 312. and "Elements of Electricity."' Timbie. 
Chapter 10. — Compiler's Note. 

The Photometer 

In the realm of practical physics, the photometer plays a 
prominent part because it is the accepted apparatus for deter- 
mining the candle-power or luminosity of electric lamps or other 
lighting device- as expressed in terms of a standard lamp or 
some other established value of light. Of course the traditional 
standard candle is obsolete, and the amylacetate standard lamp 
has also been relegated to oblivion: both giving place to the 
incandescent lamp of known illuminating power. 

In view of the fact that the decrease in efficiency of an in- 
candescent lamp is large when carrying an underload, and that the 
life of the filament is shortened enormously by an overload. 
stress should be laid upon the reason for marking a lamp so as 
to indicate its correct e.m.f. 

It gives us pleasure to find that many high schools use the 
photometer in their physics course, and that we are therefore 
able to present the results of tests made by high-school students. 

EXPERIMENT NO. 8 

AN EXERCISE IN PHOTOMETRY 

Mr. Lewis H. Ee~. Head of the Science Department of the 
Everett High School. Everett, Washington, contributed the fol- 
lowing excellent exercise, -gether with the comments, direc- 
tions and conclusions relating thereto, which we produce ver- 
batim : 

"The following laboratory problem is one of a list of those 

required of all regular physics students in the Everett High 

School. The followir- : data is about an average of the 

be a a whole. No originality is claimed for the problem 

and the only excuse for its publication is to offer one of the 



AN EXERCISE IN PHOTOMETRY 



29 



problems which show the correlation between the laboratory 
work in light and electricity. 

"Directions. Set up the apparatus as in the accompanying 
sketch. Have your set-up checked by the instructor before 
closing the switch. Move the screen along the scale until the 
two sides are equally illuminated. Read the distance from 
the unknown lamp; and since the scale is 100 cm. long, if you 
subtract this reading from 100 you will have the distance from 
the standard. Make three or four determinations of this dis- 
tance and use the average in the equation: 

c.p. of standard : c.p. of unknown : : L 2 : I 2 , 
where L = distance from screen to standard lamp and 
I = distance from screen to unknown lamp. 




Fig. 10. — An Exercise in Photometry. Fee's Method. 
Instruments Used were two Model 156 Weston Ammeters, and a Model 
155 Weston Voltmeter. This outfit may also be used with direct current. 

"This equation is derived from the well-known law, 'The in- 
tensity of illumination varies inversely as the square of the dis- 
tance.' Since the intensity is the same at the screen, the intensity 
or c.p. of the source must vary directly as the square of the dis- 
tance. 

"The candle-power is measured at different voltages to show 
that there is a relation between the voltage and the candle-power. 
Lamps of different kinds and ages were used to gain some idea 
of economy in electric lighting. 

"Apparatus. A home-made photometer. (This photometer 
is merely a rectangular box 16X16XH6 cm. with doors at either 
end for the insertion of the lamps and also one near the center 
for moving the screen. See Fig. 10. 



30 



EXPERIMENTAL ELECTRICAL TESTING 



"The screen is made of two cakes of paraffin separated by 
a piece of tinfoil and held before a window cut in a rectangular 
metal box 5X^X12 cm. The ends of this metal box are open 
towards the lamps that are placed in either end of the large 
box. It is 100 cm. from center to center of the lamp sockets. 

"Two slide resistances. 

"Two Weston A.C. ammeters, Model No. 156. 

"One Weston A.C. voltmeter, Model No. 155. 

"One standardized incandescent carbon lamp 31.03 c.p. at 
105 volts. 

RESULTS 



Carbon 



Volts 


105 


95 


85 


Amperes 


0.76 


0.72 


0.65 


Distance to screen 


50.9 cm. 


46 . 4 cm. 


41.4 cm. 




50 . 5 cm. 


46 . 4 cm. 


41.6 cm. 




50.5 cm. 


46.0 cm. 


41.4 cm. 


Approximate age in hours of use. . . 


New 


New 


New 


Rating 


100 watt 


100 watt 


100 watt 


Candle-power 


32.69 


23 01 


15.58 


Per cent decrease in voltage 




9.5 


19 


Per cent loss in c.p 




29 


52 









Carbon 



Volts 

Amperes 

Distance to screen. 



Approximate age in hours of use 

Rating 

Candle-power 

Watts per c.p 

Per cent decrease in voltage 
Per cent loss in c.p 




85 

0.70 
36.1 cm. 
36.0 cm. 
37.3 cm. 
1000 
32 c.p. 
10.55 

5.64 
19.0 
65 



Mazda 



Volts 


105 


95 


85 


Amperes 


0.35 


0.35 


0.35 


Distance to screen 


51.3 cm. 


47.6 cm. 


42.4 cm. 




51.0 cm. 


47.2 cm 


42.3 cm. 




50.5 cm. 


47.0 cm. 


43.0 cm. 


Approximate age in hours of use . . 


New 


New 


New 


Rating 


40 watt 


40 watt 


40 watt 


Candle-power 


33.43 


24.94 


17.05 


Watts per c.p 


1.10 


1.37 


1.74 


Per cent of decrease in voltage .... 




9.5 


19 


Per cent loss in c.p 




23 


49 



AN EXERCISE IN PHOTOMETRY 



31 



Mazda 



Volts 

Amperes 

Distance to screen. 



Approximate age in hours of use. 

Rating 

Candle-power 

Watts per c.p 

Per cent decrease in voltage 

Per cent loss in c.p 



105 
0.40 
41.4 cm. 
51.0 cm. 
51.4 cm. 
500 
40 watt 
34.35 
1.22 



95 

0.40 
47.0 cm. 
46.7 cm. 
46.5 cm. 
500 
40 watt 
23.88 

1.59 

9.5 
30 



85 

0.40 
42 . 1 cm. 
41.0 cm. 
41.5 cm. 

500 
40 watt 
15.65 

2.17 
19 
54 



Conclusions 

" In order to arrive at any definite conclusions it would be 
necessary to test a large number of lamps, hence the conclusions 
arrived at here are only approximate. 

"Incandescent lamps should be operated at nearly their rated 
voltage as the c.p. decreased approximately three times as fast 
as the voltage. It is also more economical, as is shown by the 
'watts per c.p.' 

"That the metal filament is the more economical since the 
'watts per c.p.' are only about one-half what they are for the 
carbon filament. 

"That in the old carbon lamp there was not only a decrease 
in c.p., but also an increase in current consumption, making it 
expensive to use. 

"That the metal filament lamps are less affected by age and 
change of voltage than are carbon filament lamps." 

(Signed) Walter Sundstrom, 
Grant Durkee. 



Quiz for Students. Include a switch in the main line so 
that current will flow through a metal filament and a carbon 
filament lamp simultaneously when the circuit is closed. Note 
that the light from one lamp "arrives" at the screen more 
quickly than from the other; and that the light from one source 
also disappears sooner when circuit is broken. Why? 

Does the light from one lamp travel more quickly than the 
other? — Compiler's Note. 



32 EXPERIMENTAL ELECTRICAL TESTING 

EXPERIMENT NO. 9 
PRACTICAL INCANDESCENT LAMP TESTING 

(Prepared by the Compiler.) 

The following experiments have a direct bearing on some 
of the problems encountered in the practical construction and 
testing of incandescent lamps. 

They also serve to illustrate that a thorough mastery of 
the characteristics of Weston instruments is no insignificant 
accomplishment. 

Mount a lamp socket with leads on a board having dimen- 
sions of about 3X6 inches. 

Screw in a 32- or else a 16-c.p. common carbon filament 110- 
volt incandescent lamp.* 

(1) Connect leads with a Wheatstone bridge or any portable 
test set, and measure the resistance of the lamp at room tem- 
perature. Record resistance and temperature. 

(2) Substitute a 60- or a 40-watt metallic filament lamp and 
repeat the test. Record results. 

Connect the leads with a d.c. service line.t 

Include in the circuit the carbon lamp, the 1.5 ampere range 
of a Weston Model 280 ammeter, and a snap or knife switch. 
Also connect a voltmeter of suitable range across the terminals 
of the socket. 

(3) Close the switch and let the current flow for about five 
minutes. Then break and instantly remake the circuit, keeping 
your eye on the pointer. Note that it will overswing slightly, 
before becoming steady. Why? 

Notice the '"dead beat" action of the pointer, and the rapidity 
with which it will assume its true position. Record in scale 
divisions the extent of the overswing. Record also voltage, and 
current consumed when pointer is steady. 



*The "Gem" or G. E. Metallized Filament lamp will not serve for this 
experiment. 

tNoiE. — Direct current is necessary for these tests; but if only a.c. 
service is available, a rectifier may be used to good advantage. 



PRACTICAL INCANDESCENT LAMP TESTING 33 

(4) Open the circuit and allow the lamp to cool for at least 
5 minutes; then close the switch, watch the pointer, and study 
its action. Observe that there is now no visible overswing, but 
on the contrary a noticeable lag in its movement before it arrives 
at its position of maximum deflection. Why? Repeat test (3) 
and note that you get the same overswing as before. 

Then open the switch, wait 5 minutes- and repeat test (4). 
Record results. 

(5) Substitute a 60- or a 40-watt metallic filament lamp and 
repeat tests (3) and (4). Record all results obtained. Describe 
the action of the pointer. 

(6) Open the switch and insert the lamp almost up to its 
socket in a glass vessel containing water and cracked ice or 
snow. (A i^-gallon battery jar will do nicely.) Unless the leads 
and socket are waterproof, see that they remain dry. If water 
accidentally gets into the socket, unscrew the lamp and care- 
fully dry all parts. Measure the resistance of the filament by 
means of a Wheatstone bridge or any other test set. Record 
results, giving resistance, and temperature of solution. The 
latter should be near 0° C. Repeat (6), substituting the carbon 
filament lamp. Let this cool for at least 40 minutes before 
recording resistance and temperature. 

(7) State what strike you as the most significant character- 
istic differences between these filaments as revealed by the bridge 
measurements, (1), (2) and (6). 

(8) Apply Ohm's law. Determine the respective currents 
which will flow through the filaments at room temperature, and 
at the temperature of melting ice, according to this law, when 
e equals voltage at the socket as previously recorded in tests 
(3) and (5), and r equals values obtained by bridge measure- 
ments. Compare the calculated current obtained at room tem- 
perature with the ammeter indications in the preceding tests (3) 
and (5) ; when current was steady; and if there are any differ- 
ences state why. 

(9) In any test, did any swing of the ammeter point indicate 
a current which was equal to or greater than the current which 
should flow, as obtained by calculation according to Ohm's law? 

(10) Use any portable current indicator obtainable, in place 
of a Weston ammeter, and repeat tests (3) and (4) with it if 



34 EXPERIMENTAL ELECTRICAL TESTING 

possible. If the range of the instrument is too high to get results 
with one lamp, use several in parallel. Record results. 

(11) Explain the characteristics of the Model 280 ammeter 
that make it the most satisfactory portable instrument for these 
tests. Base your statements solely upon the results you have 
obtained. Do not generalize, or attempt to describe the instru- 
ment in detail. 

(12) Answer the quiz question under photometer experiment, 
and explain its correlation to test (4) . 

ELECTROPLATING 

Department of Physics. State Normal School, 

Bellingham, Washington. 

Dec. 12. 1913. 
Weston Elect. Ixst. Co.. 
Newark, New Jersey. 
Gentlemen. — In accordance with the request in your last 
communication, I am mailing you a student's laboratory report 
on the electro-deposition of copper. Although the student under- 
stood the experiment thoroughly his discussion is somewhat 
meager. I have indicated my chief criticisms.* 

I do not believe in stereotyped forms of reports. I like to 
leave as much as possible to the judgment of the student, call- 
ing for additional discussion either orally or in writing, if not 
enough is given. 

In this experiment I usually find the current obtained from 
the a.c. mains and Nodon valve constant enough to justify 
taking a number of amperage readings and striking an average. 
In the second test of this report the current varied over so 
great a range f (from .85 amp. to 1.1 amp.) that it was neces- 
sary to note the length of time that it stood at each value and 
to compute the total number of ampere-seconds from the several 
amperages and the corresponding times. 
Very respectfully, 

(Signed) H. C Philippi. 

*Mr. Philippi states: "This boy has had only one year's work in 
Physics, taken when a sophomore in Normal School. Age 18 years." 

" tVariation in current strength was probably due to rise in temperature 
of the rectifier, or to partly exhausted solution. 



ELECTROPLATING WITH COPPER 



35 



EXPERIMENT NO. 10* 
ELECTROPLATING WITH COPPER 

"In electroplating with copper, how long will it take one 
ampere of current to deposit one gram of copper? What is the 
electro-equivalent of copper? 

"The alternating current of the city lighting system is changed 
to a direct current by means of the electrolytic alternating cur- 
rent rectifier. See Fig. 11. 




WttW 




Fig. 11. — Electroplating with Copper. Philippi's Method. 
Apparatus Includes an Electrolytic Rectifier and a Model 280 Weston 

Ammeter. 



"The strength of the current is regulated by being run through 
the bank of incandescents. 

"Difficulty was experienced in taking the second set of read- 
ings because of the inconstancy of the current, which fluctuated 
between 0.85 amp. and 1.1 amp. 

RESULTS 



Wt. of copper deposited 

Time of deposit 

No. of amperes 

Time 1 amp. will deposit 1 gm 
Electro-equivalent 



Trial (1) 



. 453 gm. 
20 min. 
1.15 

50.77 

.0003283 gm. 



Trial (2) 



.568 gm. 
30 min. 

51.36 

.0003245 gm. 



*This experiment is of special importance because a Nodon valve was 
used in connection with it. See page 53. — Compiler's Note. 



36 EXPERIMENTAL ELECTRICAL TESTING 

"No satisfactory average could be found for the amperage 
in the second trial owing to the variation in the current. 

'The amount of any metal which a current of one ampere 
will deposit in one second is called the electro-equivalent of 
the metal. For one metal this amount is always the same. Con- 
sequently this is a very accurate way to measure electricity. 
(Current strength.) 

" (Signed ) L. 0. Greene." 

March 6, 1913. 

Instructors' appended comments: 

"The method of dealing with the varying current should have 
been explained. 

"In which direction does the metal in a plating solution 
always travel? Upon which electrode is it deposited?" 



Copper plating is of great commercial importance because 
iron and steel are always plated with copper before giving them a 
finishing coat of nickel. — Compiler's Note. 

EXPERIMENT NO. 11 

THE ELECTROCHEMICAL EQUIVALENT OF A 

METAL 

Substantially the same experiment as the foregoing is given 
herewith. It was contributed by Mr. Arthur H. Killen, In- 
structor in Physics, Flushing High School, Flushing. New York. 

This experiment was performed and the report written by 
one of the senior students.* It was accompanied by a very 
creditable sketch which we reproduce. (See Fig. 12.) 

Experiment. To find the electrochemical equivalent of a 
metal. 

Object. To find the electrochemical equivalent of copper. 

Apparatus. Two strips of copper, a copper sulphate solu- 
tion plating bath, a Daniell cell, a Weston ammeter, wire, wire 
connectors. 

*Mr. Killen informs us that the student's age was IS years. 



ELECTROCHEMICAL EQUIVALENT OF A METAL 37 

Work Done. I carefully weighed a strip of copper which 
was to be plated. I connected, in series, the Daniell cell, the 
Weston ammeter and the two strips of copper (the one care- 
fully weighed) and another which had been placed in the copper 
sulphate solution electroplating bath. At intervals of one min- 
ute, I took readings of the Weston ammeter during forty minutes 
and averaged them to find the amperage or current strength 
during the forty minutes. I then removed the strip on which 



SULFHURIC 
ACID SOLUTION 



DANIELL CELL 



COPPER ON WHICH PLATE 
IS TO BE DEPOSITED 




COPPER FROM WHICH 
PLATE IS TO BE TAKEN 



Fig. 12. — The Electrochemical Equivalent of a Metal Test. (Repro- 
duced from Student's Sketch.) Killen's Method. 

Instrument Used was a Model 1, Weston Standard Ammeter. Range 
2 Amperes. 

the copper was deposited from the electroplating bath and care- 
fully rinsed and dried it. I then reweighed it. 

Observations : 

Weight of strip to be plated 22.952 grams 

Weight of strip to be plated after forty 

minutes 23.532 grams 

Amount deposited in forty minutes 58 gram 

Average amperage or current strength 73 ampere 

Amount deposited by .73 ampere in one hour. .87 gram 

Amount deposited by 1 ampere in one hour. . 1.191 grams 
Amount deposited by 1 ampere in one second. .0003308 gram 



Conclusions. The electrochemical equivalent of copper is 
.0003308 gram, that is .0003308 gram of copper is deposited 
by one ampere in one second. 



38 EXPERIMENTAL ELECTRICAL TESTING 



Mathematical Work 

1st weight of object to be plated 22.952 grams by .73 amp. 

Weight of object to be plated after 

forty minutes 23.532 grams by .73 amp. 

Weight of deposit at end of 40 minutes . .58 gram by .73 amp. 

58 
-^=.0145, wt. deposited in one minute by .73 ampere. 

.0145X60=. 87, wt. deposited in one hour by .73 ampere. 

87 
-i=~=1.191+wt. deposited by one ampere in one hour. 

1.191 

-^—— =.00033083, wt. deposited by one ampere in one second. 

Sylvanus Thompson gives .0003281 as the electrochemical 
equivalent of copper. 

(Signed) Henry Greenberg, 

(A. H. K., Instructor.) 



THE USE OF THE ELECTRIC HEATER IN 
EFFICIENCY TESTS.* 

By Ernest Reveley Smith, Syracuse North High School. 

We are living in an age of commercialism. The relation 
of output to input is the great factor which determines our 
investments whether large or small. What is so general about 
us cannot fail to enter our laboratories. The toys that have 
been used so long as equipment are rapidly disappearing, their 
purposes well served. In their places are coming the newer 
commercial appliances, the experimental uses of which commend 
themselves instantly to the boy or girl as something worth while. 

Among the commercial offerings to the Physics laboratory, 
few have greater possibilities than the various types of electric 
heaters. The very fact that the electric stoves, flatirons, immer- 
sion heaters, etc., are taking their places among the things of 
our every day life makes the use of them in the laboratory both 
interesting and profitable. 



♦Reprinted from School Science and Mathematics, Vol. 13, 1913. Avail- 
able through the courtesy of the author. — Compiler's Note. 



THE ELECTRIC HEATER IN EFFICIENCY TESTS 39 



Also they are the most adaptable of any of the laboratory 
equipment for work along efficiency lines, since all that is neces- 
sary for performing the experiment, besides the heater itself 
and the sources of current, is common equipment found in every 
laboratory. Generally we use an electric stove, with a voltmeter 
and an ammeter of suitable ranges, a flat bottom aluminum 
sauce pan, a watch and a thermometer. 

The ammeter is connected in series with the stove and the 
voltmeter shunted across its terminals, see Fig. 13. (A watt- 
meter may be used in place of these instruments.) While the 
kettle, and the kettle with the water are being weighed, the cur- 
rent is turned on through the stove, so that it may come up to 



VOLTMETER 




Fig. 13. — Instruments Shown are Weston Model No. 1, Voltmeter 
and Ammeter. Alternating Current Apparatus may be Substituted. 

the normal working temperature. In this way very little heat 
is absorbed by the stove itself during the actual tests. 

The temperature of the known weight of water is now taken 
and the kettle placed on the stove just as the stop watch is 
started. Voltmeter and ammeter readings are taken every min- 
ute and their average readings used, since there is usually con- 
siderable variation in the potential of city currents. At the end 
of a given time (ten minutes), the temperature of the water is- 
read after stirring, and the current is cut off. 

From the average current and fall of potential through the 
stove, its resistance is computed. The heat developed in the 
stove is computed from the well-known formula, calories= 
0.24iC 2 Rt. The water equivalent of the kettle is found from 
its mass and specific heat. Then the heat absorbed is the mass 



40 



EXPERIMENTAL ELECTRICAL TESTING 



of the water including the water equivalent of the kettle, multi- 
plied by the change in temperature. The efficiency is now 
obtained by dividing the calories absorbed by the calories devel- 
oped. 

The efficiency tests that have been made in our school for the 
past three years have given results varying from 45 to 50 per 
cent with one stove and from 65 to 70 per cent with another. 

This experiment may be varied in several details. The 
apparent efficiency will be raised from 10 per cent to 15 per cent 
by using a large amount of water in place of 400 or 500 grams. 
Covering the kettle will usually raise the results by 3 per cent 
or 4 per cent. Again enclosing the kettle and stove in an asbestos 
jacket will give a result some 5 per cent to 10 per cent higher. 
This jacket is easily made from asbestos sheeting. Another 
variation brings into use the heat of vaporization. The experi- 
ment is continued until part of the water has boiled away. The 
kettle and contents are then weighed. The heat absorbed is 

equal to the sum of the heat 
necessary to bring all the water 
to the boiling point and that 
required to vaporize the water 
lost by boiling. This method 
will give results slightly higher 
than the first. 

The immersion heater (see 
Fig. 14) gives much higher re- 
sults than the stove. Our tests 
have shown an efficiency vary- 
ing from 90 per cent to 98 per 
cent. The heater is tested in the 
same way as the stove. For 
general use about a laboratory 
this device is very satisfactory as it will heat water more quickly 
than gas and may be used with any kind of a dish. 

The flatiron makes an excellent stove. In fact, many manu- 
facturers furnish a stand to hold it inverted as well as a dish 
shaped to fit its working surface. Its efficiency is not as high 
as the immersion heater or stove, ranging from 40 per cent to 
60 per cent, depending largely upon the shape of the kettle. 




Fig. 14. — The Immersion Heater 



THE ELECTRIC DISK STOVE OR HOT PLATE 41 

In laboratories having electricity but no stove, an incandescent 
bulb may be used for efficiency tests. If the experiment is per- 
formed first with a covered opaque calorimeter, and then with 
a glass jar, the relative amounts of energy given off as heat and 
light may also be determined. 

In any of the above experiments the cost of electricity may 
be easily computed. If the pupil has found, earlier in his work, 
the cost of using a gas stove or burner for a similar length of 
time, he now has data for an interesting comparison. 

Usually I divide the class into several squads of five or six 
for these experiments. While one squad is performing this experi- 
ment the other members of the class are working on an ex- 
periment for which we have individual apparatus. One pupil 
from each squad weighs the kettle and water, another reads 
the thermometer, another has charge of the wiring, while others 
read the voltmeter and ammeter or hold the watch. This insures 
the constant attention of each member of the squad since he 
has something to do which is definite and vitally important to 
the experiment. Of course, the entire experiment may be per- 
formed by two pupils, if desirable, or made a class exercise, 
letting several pupils make the readings for the class. Which- 
ever way it is done, it furnishes one of the most instructive as 
well as popular experiments in our laboratory. 

EXPERIMENT NO. 12 

THE ELECTRIC DISK STOVE OR HOT PLATE* 

Contributed by Mr. H. C. Philippi, Head of Science Department, State 
Normal School, Bellingham, Washington. 

Object. To determine the efficiency of an electric disk stove 
or hot plate. 

Apparatus. Electric disk stove; Weston voltmeter; Weston 
ammeter; two-quart copper tea-kettle; thermometer; balance 
and weights; watch. See Fig. 15. 



♦Contributor states: "The results are those actually obtained by 
members of my class." — Compiler's Note. 



-:. 



:---::: L electrical testing 



For convenience in making connections the ping and flexible 

:::i ire re~:~"ec ::::_ ~n c ::~e ::t ;;:""f z::_Li.:ei urei 3, 
board and its terminate permanently attached to binding posts 
— ±e :::.:i Tie ::iir::::: ; ire. :■: ::_:se :i:se ::' nr 

e-e::r::;C i:~e: eee: Be:: re niLiiz ::.e :ee: --:':. is :: 




_-::- . — 



r'l_'.7l 



- 
j eeeny ::. 

:e Lire! :■: 



COST OF OPERATING AN ELECTRIC FLAT IRON 43 



RESULTS OBTAINED BY STUDENTS 





Trial (1) 


Trial (2) 


Trial (3) 


Weight of water used 

Weight of tea-kettle 

Water equivalent of tea- 
kettle appr 


4.4 1b. 
1.01b. 

0.11b. 
66.2° 
129.2° 
63.0° 
107.0 
4.95 
10 min. 
283.5 
530 

318,000 

301.4 B.T.U. 

94.0% 
94.4% 

5.3c. 


4.41b. 
1.01b. 

0.11b. 
59.0° 
123.8° 
63.8° 
107.0 
4.95 
10 min. 
287.1 
530 

318,000 
95.2% 


4.41b. 
1.01b. 

1 lb 


Initial temperature Fahr. .. 
Final temperature 


59.9° 
123.8° 


Rise in temperature 

Average voltage applied — 
Average current in amp.. . . 
Time current ran 


62.9° 
107.0 
4.95 
10 min. 


Heat gained (B.T.U.) 

Power input (watts) 

Energy input (watt-sec.) 
(Joules) 


283.0 
530 

318,000 
93.9% 


Heat equivalent of this en- 
ergy 1055 watt-sec. = 
1 B.T.U 

Efficiency of stove & kettle. . 

Average efficiency 


Cost per hr. to operate this 
stove at 10c. per kw. hr. . . 





EXPERIMENT NO. 13 

COST OF OPERATING AND EFFICIENCY OF AN 
ELECTRIC FLAT IRON 

Contributed by Mr. F. H. Beals, Barringer High School, Newark, N. J. 

Object. To determine (1) Cost of ironing roller towels. (2) 
Efficiency of an electric flatiron. 

Apparatus. Electric flatiron weighing 5.8 pounds rated as 
weighing 6 pounds and using 110 volts and 4.2 amperes, ironing 
board 38"X14%", having no padding but covered with a roller 
towel stretched over the surface, dampened towels, Weston 
wattmeter (150 volts and 5 amperes) , fuse blocks and connections, 
balance, scales and weights. See Figs. 16 and 17. 

Performed by Elizabeth Arculaeius. Assisted by Ruth 
A. Husk and Katherine Van Alen. 

Manipulation 
Directions. Sprinkle towels in preparation for ironing. 
Connect up iron and wattmeter as shown in diagram, Fig. 17. Let 
the current run 2% minutes to heat the iron. Iron rapidly so 



44 



EXPERIMENTAL ELECTRICAL TESTING 



as to waste as little heat as possible. To find the number of 
calories required to evaporate water, allow 80 calories per gram 
to heat from room temperature to temperature of evaporation, 
and 536 calories to evaporate water. Let A represent output 
in calories=loss of weight X (536+80 L To find heating power 
of current, let B represent input in caloriesr=wattsXsec.X-24. 
To find efficiency use A-^-B. To find cost allow 10 cents per 
K.W. hr. Cost=watts-^1000xhr.Xl0c. 




■ -; . ■ . - . - •• ■ ••■ ■•■•■• -•■:••■ ■ ■ 



TO LINE 




Fig. 17. — Beals' Wattmeter Method. (Reproduced from Connection 

Chart.) 

Instrument used ^vas a Model 310 Weston Wattmeter. Ranges 5 
and 10 Amperes and 75 and 150 volts. 



Method. General Principle: After the towels were damp- 
ened and weighed, the ironing was commenced. The wattmeter 
was read at regular intervals and recorded. When the towels 
were ironed they were weighed again. The length of time taken 
for ironing was also noted. The average number of watts was 
found, and the loss of weight in grams due to evaporation was 
determined. Throughout the experiments readings were taken 
as recorded below. 

Case I. A wet towel was used. In finding the efficiency 
no allowance was made for evaporation or absorption. 




CQ 



COST OF OPERATING AN ELECTRIC FLAT IRON 45 

Case II. Conditions the same as in Case I. 

Case III. Five towels were dampened the evening before 
as for ordinary ironing. In finding the efficiency no allowance 
was made for evaporation or absorption. 

Case IV. A very damp towel was used. In finding the 
efficiency allowances were made: (1) For evaporation, due to 
the heat of the room, that would have taken place in the 8V2 
minutes without ironing. (2) For absorption of moisture by 
towel covering board. (3) For evaporation (while airing 4 
minutes) due to heat of towel, above room temperature. 

No allowance was made for heating the iron. The temper- 
ature of the room was 22° C. It may be of interest to know 
that the relative humidity for the day was 55 per cent, but this 
was not used. 

DATA AND CALCULATIONS 

No allowances for correction 



Case. 


I 


IT 


III 


Condition of towel 


1 wet 
413.0 g. 
273.5 g. 
139.5 g. 
531.5 

13.5 min. 

80.1% 

$0,012 


1 very wet 

421.2 g. 

268.3 g. 
152.9 g. 
541.3 

15.0 min. 
80.6% 
SO. 013 


5 slightly wet 
1255.4 g. 
1180.6 g. 


Weight wet 


Weight ironed 


Loss of weight 


74.8 g. 
535.0 


Watts average 


Time taken for ironing .... 

Efficiency 

Cost of ironing towels 


8 . 5 min. 
70% 
$0,007 



Allowance for corrections 



Case 



IV 



Condition of towel 1 very damp 

Time to heat iron 1.5 min. 

Watts — average 531 . 

Weight wet 382.9 g. 

Weight ironed. 234 . 4 g. 

Loss of weight by ironing 148 . 5 g. 

Time actually consumed in ironing 10.0 min. 

Weight of towel covering board (before ironing) 233 . 9 g. 

Weight of towel covering board (after ironing) 247 . 6 g. 

Increase in weight of towel covering board 13 . 7 g. 

Weight of towel immediately after ironing 234 . 4 g. 

Weight of towel dampened to same degree as one ironed 382.9 g. 

Weight of same towel hanging 8 3^ min. in air 366.6 g. 

Loss of weight in this second towel 15 . 3 g. 

Efficiency 88.5% 

Cost of ironing one very damp towel $0 . 007 



46 EXPERIMENTAL ELECTRICAL TESTING 

Efficiency. Case I. 

139.5X^536+80) 85932 

-=83.2%. 



x II. 



Case III. 



531X13.5X60X-24 103226.4 
152.9X (536+80) 94186.4 



541.3X15X60X.24 116920.8 
74.8X (536+80; 46076.8 



-=80.6%. 



535X8.5X60X-24 65484 



=70.4%. 



Case IV. 

(148.5—13.7—15.3) (536+78) 73373 

= =96.0% . 

531X10X60X-24 76464 

Conclusion. It seems to me that the reason why the effi- 
ciency is lower in Case III is because the amount of moisture to 
be evaporated is not so great in this case as in the others. Cer- 
tainly the cost of ironing depends upon the quantity of water 
used in sprinkling. 

The cost of ironing five towels moistened as in ordinary 
ironing was found to be 0.7 cent. 

Computations were checked by George Y. Sosnow. 

It may be of interest to observe that the above method of 
measuring efficiency by the amount of water evaporated has 
been used at the Barringer High School to obtain the efficiencies 
of an electric toaster and an electric stove, and conversely to 
obtain the latent heat of vaporization. 

The highest efficiencies were obtained when there was con- 
tact, as in the case of the electric flat iron, and the lowest when 
the heating was chiefly by radiation, as in the electric toaster. 

Domestic electrical contrivances are not of course primarily 

med to serve as a means of affording physical quantities 

which may be readily determined with scientific exactness; but 

rather to permit useful work to be performed with expedition, 

convenience and minimum cc s 

Hence individual results obtained from different sources may 
disagree, without, however detracting from their educational 
value. 



BOILING AN EGG BY MEANS OF ELECTRICITY 47 

EXPERIMENT NO. 14 
BOILING AN EGG BY MEANS OF ELECTRICITY 

Contributed by Mr. Ernest R. Smith, Vice-Principal of the Syracuse North 
High School, Syracuse, N. Y. 

Object. To find the cost of boiling an egg by means of 
electricity and incidentally to determine the efficiency of the 
stove. 

Apparatus. Small disc stove; Model 155 Weston Voltmeter; 
Model 155 Weston ammeter; aluminum kettle; thermometer; 
platform balance and weights; eggs; watch and source of A.C. 
current. 

Results. 

Weight of kettle 215.4 grams 

Weight of kettle and cold water 1222.6 grams 

Temperature of cold water 23.8° C. 

Weight of kettle and contents after boiling 

egg for (3) min 1151 grams 

Temperature of boiling water for day 99.45° C. 

Temperature change of water 75.65° C. 

Fall of potential through stove 112 volts 

Current through stove 5.31 amps. 

/ E\ 

Resistance of stove i? =- ) 2109 ohms 

V C J 

Heat developed in stove in 20 minutes=.24 

C 2 Rt=.24:X (5.31) 2 X21.09X20X60 171,336 cal. 

Water equivalent of kettle (MX&) ; • 47.4 grams 

Heat absorbed by water in coming to the boil- 
ing point, 1054.6X75.65 79,780.5 cal. 

Heat used in boiling away 71.6 grams of water' 

71.6X537 38,449.2 cal. 

Total heat absorbed by water 118229.7 cal. 

Output 118229.7 

Efficiency of stove= = 69% 

Input 171,336 
112X5.31 

Kilowatt-hours of work X% -198 kwt. hr. 

1000 
Cost of operating stove to boil egg for 3 min- 
utes at 8c per kwt. hr 1.6 cts.* 

December 8, 1913. (Signed) Delphine Be Quillard. 

*Several eggs might have been cooked at a very slight increase over 
the above cost for one, as the dish and quantity of water were sufficiently 
large. — Instructor's Note. 



4S EXPERIMENTAL ELECTRICAL TESTING 

Manipulations. The small electric stove was connected 
to the a.c. main and an ammeter put in series with it and a 
voltmeter shunted across its Terminals. I found the weight of 
the kettle empty, and filled two-thirds full of cold water, 
taking the temperature of the water, the kettle was placed on 
the stove and the current turned on. Readings of the volt- 
meter and of the ammeter were taken every minute. "When 
the water began to boil the egg was put in and the boiling con- 
:r;ri ::: :iir™ :i±lu:^. 

The kettle and ho: water were weighed again. From the 

barometer reading, the temperature of boiling water for the 

".;-- — :.; ir^rmined. The >:cnipu::.:::^5 :- ::_'.:: :-. i in :h€ 

tabulation were made. The cost of boiling the egg was found 

to be 1.6 cents and the efficiency of the stove 69 per cent. 

EXPERIMENT NO. 15 

THE IMMERSION HEATER 
The experiment ~ - irpeated, using a smaller dish and an 
immersion heater. See Fig. 14. 



VTeigh: ;: iish 145.2 grams 

^."eigii: :: li-i: ;:::". _/,-:-: ... --"' '. r. :i_- 

7 Jperature of cold water 

Weight : : kettle and contents after boiling egg 

3 ni:"-"i:r= 4.5 mii".::-^ -_ ' '. zz: ::.- 

Temperature of boiling water for dav 99.45= C. 

Temperature change of water 75.65° 

Fall of potential through heater 111.0 volts 

::t^: \:.zvlz:. i.r 6.06 amps. 

--.Ht :: le :er IS. 31 ::".m^ 

:. ::: - : n:r.^:e ; = 

_4 K (6.06» 2 X1S -- 5 X60. 43.5a5.1 caL 

bsorbed by water in coming to boiling pt. 24.533.3 caL 

used in boiling awav 30 gms. of water. . 16.110.0 cal. 

Total heat absorbed 40.643.3 caL 

:encv of heater 

111X6.06 4 

Work done bv he:^er < — .05 kwt. hr. 

1000 60 

of boiling egg at 8c per kwt. hr 0.4 ct. 

December 8, 1913. S gned» Delphixe Be Qvillahd. 

Fig. IS I .ilippi's arrangement* for suitable diagram of 
connections containing instruments used. — Compiler's Note. 



MAKING COCOA AND CANDY 



49 



EXPERIMENT NO. 16 

MAKING COCOA AND CANDY WITH THE AID OF 
ELECTRICITY 

Contributed by F. H. Beals 

Object. To find the cost of making Cocoa and Candy 
(Fondant) and of boiling water on the electrical disk stove; also 
determining the efficiency of the stove. 




HUBBEL PLUG 



10 AMP. FUSE 



Fig. 18. — Beals' A. C. Voltmeter and Ammeter Method. (Reproduced 
from Connection Chart.) 

Instruments used were Model 156 Weston A. C. Voltmeter, range 150 
Volts and Model 156 Weston Ammeter, range 10 amperes. 



Apparatus. Weston Voltmeter and Ammeter, Disk Stove, 
Double Boiler, Thermometer, Graduate. See Fig. 18. 
Performed by Helen Burnett and Marion Butler. 



50 



EXPERIMENTAL ELECTRICAL TESTING 



Making Cocoa, 
Experiment A. 



Case I 
Ingredients 

Cocoa, 8 level tea- 
spoonfuls. 

Sugar, 6 level tea- 
spoonfuls. 

Cold water, 2 cups 
(500 c.c). 

Cold milk, 2 cups 
(500 c.c). 

Method 

Pour the cold milk 
and water into the 
metal boiler on the disk- 
stove. Make the elec- 
trical connections as 
shown on the sketch; 
record time and turn 
on current. 

Mix the cocoa and 
sugar well together in 
a bowl; add H cup of 
cold water and stir to 
make a thin paste. 

Pour some of the hot 
mixture into the bowl 
and wash out all the 
cocoa into the boiler. 
Bring to a boil and boil 
three min. 

Case II 
Ingredients 

Cocoa. 3 level table- 
spoonfuls. 

Sugar. 3 level table- 
spoonfuls. 

Water, 2 cups (500 
c c ) 

Milk, 2 cups ( 500 c.c). 
Method 

Mix cocoa, sugar, and 
water thoroughly. 

Bring milk to boiling 
point; add first mix- 
ture and bring all to 
scalding point. (About 
80 : C.) 



Making Fondant Candy, 
Experiment B. 

Ingredients 

Sugar, 1 cup (2 oz.). 

Water, % cup (96 c.c.) . 

Cream of tartar, %6 
teaspoonful. 

Method 

Mix sugar, cream of 
tartar, and water to- 
gether in lower part of 
double boiler. Place on 
the disc-stove, having 
had the current on 2 
min. to allow for heat- 
ing. Record time. 

Stir mixture until 
sugar is completely dis- 
solved, boil uncovered 
until a drop of the mix- 
ture dropped from the 
end of a spoon spins a 
thread, or until it forms 
a thick, jelly-like con- 
sistency when dropped 
into cold water. 

Turn off current, first 
recording time. Pour 
the mixture upon a 
well-greased marble slab 
or a flat platter. When 
sufficiently cool so that 
the mixture does not 
adhere to the finger 
when touched in the 
center, beat with wood- 
en spoon until the mix- 
ture becomes too hard 
to beat, then knead 
with the hands. When 
it becomes sufficiently 
cooled, roll into small 
balls for bonbons. 



Boiling Water, 
Experiment C. 



Case I 

1000 c.c of water in 
the lower part of the 
double boiler, and upon 
the disk-stove. 

Bring to boiling point, 
recording time taken 
to perform experiment. 

Case n 
Place 250 c.c. of water 
in the lower part of the 
double boiler, and 500 
c.c. of water in the up- 
per part. Place both 
parts on the disk-stove, 
together and heat. Re- 
cord time taken to heat 
water in upper boiler 
and obtain other neces- 
sary data. 



MAKING COCOA AND CANDY 



51 



Time required to heat plate . 



Volts (average 

Amperes (average) 

Watts-volts amperes 

Weight of boiler 

Water equivalent of boiler (approx.) 

Water equivalent of boiler (approx. ) 

Quantity of water used 

Quantity of milk used 

Tern, of water alone after 8 min 

Tern, (cocoa and water) when fin- 
ished 

Tem. water before heating 

Tern, milk before heating 

Total time taken to make 

Cost to make 1000 c.c. of cocoa 

Cost to make 235 g. of candy 

Cost to boil 1000 c.c. of water in 
lower boiler 

Cost to heat 250 c.c. water in the 
lower boiler, and 500 c.c. of water 
in the upper boiler, i.e., cost of 
both 

Practical efficiency (water) 

Theoretical efficiency (water and 
dish) 



Outer Parts of Double Boiler. 



Both 

Parts of 

D.B. 



Cocoa, 
Experiment A. 



2 min. 
Case I 
114.5 
3.6 
412.2 
630 g. 
0.1 
63.0 g. 
(2c.)500c.c. 
(2c.)500c.c. 



92° C. 

26° O. 

15.5° C. 

24 min. 

$.016 



2 min. 
Case II 
119.0 
3.8 
452.2 
630 g. 
0.1 
63. Og. 
(2c.)500c.c. 
(2c.)500 c.c. 
100° C. 

79° C. 

25° C. 

15° C. 

14.5 min. 

$.0109 



72% 
81% 



Candy, 
Experi- 
ment B. 



2 min. 

" iis" 

3.7 

425.5 

630 g. 

0.1 

63.0; 



21° C. 
15.5 min 
$.0116 



Water, 
Experiment C. 



2 min. 
Case I 
117 

3.7 

432.9 

630 g. 

0.1 

63. Og 

1000 c.c. 



96° C. 
25° C. 



15 min. 



$.0108 



76% 
81% 



2 min. 

Case II 

117 

3.7 

432.9 

630 g. 

0.1 

63. Og. 

750 c.c. 



95° C. 
25* C. 



32 min. 



$0,023 
26% 



29% 



Conclusion. It is evident that the electric disk stove is not 
nearly as efficient when both parts of the double boiler are used 
as when the single dish is used. And also that the real efficiency 
calculated for actual heating of water is less than efficiency 
reckoned on the basis of amount of metal and water used. 



Practical efficiency=- 



Weight of water X change in temp. 



No. watts X No. seconds X -24 
Theoretical efficiency^ 

(weight of water+.l wt. of boiler) change in tem. 

No. wattsXNo. secondsX-24 

In calculating efficiency we considered two cases. 

(1) Practical efficiency, when we took into consideration only 
the heating of the water actually used and (2) theoretical effi- 
ciency, when we considered the heat absorbed by both the water 
and the dish. 



52 EXPERIMENTAL ELECTRICAL TESTING 

The cost of making 2 quarts of cocoa was about 2.7 cents; 
for making over % pound of candy, 1.16 cen* ; 

Instrttctoe's Note. The second year of science for girls 
at Barringer High School differs from the course for boys, one- 
fifth of the girls' year being devoted to cooking. The work in 
electricity for girls is correlated with this branch of domestic 
science. All the electrical experiments, except Case II above, 
were performed in the physical laboratory; the second method 
of making cocoa seemed to the Cooking Department more 
satisfactory. 

There can be no doubt that the exercises in electrical heating 
and cooking have touched the daily life and experience of the 
girls who have done them. They are incomparably superior 
to the old, conventional experiments of the physical laboratory, 
so far as the girls are concerned. 



AN ELECTROLYTIC CURRENT RECTIFIER 53 

AN ELECTROLYTIC CURRENT RECTIFIER 

(Prepared by the Compiler) 

In the following pages we devote considerable space to a 
description of an apparatus known as a Nodon Valve or Electro- 
lytic Current Rectifier. 

We were extremely surprised at being unable to find a single 
High School text-book which gave even a cursory reference to 
this subject; and although we do not manufacture apparatus 
of this type, we are publishing the results of our experiments. 

We do so because there are many schools which are limited 
to alternating-current line service, the character of which nec- 
essarily is not adapted to the performance of many experiments 
requiring direct current, which should form part of a High 
School course. 

In addition apart from its practical value as a means of 
transforming alternating current into pulsating direct current, 
the apparatus merits the careful consideration of all science 
teachers because it may be easily and cheaply constructed; 
and forms the basis of an experiment that should be included 
in every laboratory schedule. 

That there is a pressing demand for some such device is 
testified to by the numerous inquiries we have received for 
information pertaining to a simple form of rectifier; and it is a 
great pleasure to present the results of our investigations. 

While our work is not exhaustive, it furnishes ample material 
for exercises, and when practicable we should be glad to receive 
reports from instructors who decide to include the rectifier as 
part of their laboratory equipment. 

Students are certain to become interested in a method of 
converting "a.c." into "d.c," and especially will this be the 
case when it is explained how often some type of converter is 
used in practical work, when it becomes necessary, for instance, 
to charge an automobile storage battery at once, and no "d.c." 
is available. 

The Nodon valve form of rectifier has been selected for 
description, because it is extremely simple in construction, and a 
"valve" can be made in a few minutes at a trifling cost. 



54 EXPERIMENTAL ELECTRICAL TESTING 

It cannot be ranked as an efficient form of rectifier, and 
no such claim is made for it; but fortunately great efficiency in 
transformation is not a matter of vital importance in school 
laboratories, the main desideratum being to obtain direct-cur- 
rent service when required. 

Although also somewhat erratic in its behavior, in that the 
pulsating direct current it furnishes is not always steady, it 
would be difficult to find a single piece of apparatus which is 
more interesting and instructive than a Nodon Valve, when 
used in connection with accurate measuring instruments. 

The Nodon Valve 

Small Nodon Valves are inexpensive and are very easily 
made. All that is required is a jar containing a plate or rod of 
aluminum partly immersed in a saturated solution of bicarbonate 
of soda, and an inactive conductor. 

Sheet aluminum -^ inch thick costs less than $1.00 per 
square foot at retail. If it is too tough or brittle to bend easily, 
aluminum can be softened by holding over a Bunsen flame. In 
order to obtain good results it is of great importance that the 
aluminum employed is practically pure. Much of the commer- 
cial aluminum used in manufacturing condensers, etc., is adul- 
terated with zinc. 

We found that such material gave low efficiency, in some 
cases even causing the pointer of the direct-current instrument 
to vibrate to an extent likely to damage the movement. 

For experimental purposes, several of these valves were con- 
structed at the Weston laboratories. They consisted of glass 
jars 6 inches in diameter and 7 inches in height, containing 
plates of aluminum and lead. The lead plates were 10 by 2 x /2 
inches in area, and rg- inch in thickness. The aluminum plates 
were 1 inch by 10 inches, also of -^ inch thickness. 

It was found that the dimensions of the electrodes, jars, etc., 
were of no special consequence, and that equally good results 
were obtained when lead iron or carbon were used for the 
inactive pole. 



AN ELECTROLYTIC CURRENT RECTIFIER 



55 



EXPERIMENT NO. 17 
TESTING A NODON VALVE WITH DRY CELLS 

When the aluminum pole of one of these valves was con- 
nected with the carbon pole of a battery of two dry cells, and a 
voltmeter was included in the circuit, the latter indicated 1+ 
volts. See Fig. 19 (e.m.f. of cells was app. 2.8 volts). The 
pointer rapidly dropped to nearly zero, finally becoming station- 
ary at 0.11 volt. When the test was repeated with a milli- 
ammeter, the initial current was 0.40 ampere, which finally 
dropped to 0.0015 ampere, where it remained. 




D.C. VOLTMETER 



DRY CELLS 



Fig. 19. — Testing a Nodon Valve with Dry Cells. 

The initial current is of course affected by resistance of in- 
strument and leads, the dimensions of the valve, etc. 



The Action of a Nodon Valve 

The reason why a Nodon valve permits a flow of current 
practically in only one direction is substantially as follows: 

When a direct current is passed through a solution made 
of bicarbonate of soda, ammonium phosphate or any similar 
alkali, by means of two pieces of immersed iron, lead or carbon, 
it will be found that gas bubbles form on the plates, anct will 
rise freely to the surface. If alternating current be used instead, 
almost no gas is formed. In either case the liquid acts as a re- 
sistor, which can be shown by connecting an ammeter in series 
and changing the distance between the plates. The temperature 
of the solution is raised by the passage of the current. 

When, as stated in Experiment No. 17, a strip of aluminum 
takes the place of one of these lead or carbon plates, it will be 



56 EXPERIMENTAL ELECTRICAL TESTING 

found that the current will still flow freely when the circuit is 
completed with the (+) plus pole of the battery connected with 
the lead or carbon. 

But, if the -f- pole is connected with the aluminum, the 
initial current rapidly diminishes. This is partly due to the 
fact that gas bubbles form on the aluminum plate and rise to 
the surface of the liquid as they are crowded off by others. 
These gases are oxygen and hydrogen. In this respect, the action 
of the valve resembles that of an ordinary simple cell consisting, 
for instance, of plates of zinc and copper, dipped in an acid 
solution. But there is another and more complex action taking 
place. Substantially, the aluminum is attacked by these gases, 
which combine with it to some extent, and form upon its surface 
a non-conducting layer of hydroxide of aluminum. If the alu- 
minum plate could be completely covered with this hydroxide, it 
would practically become a non-conductor, and almost all elec- 
trical transmission would cease. 

The fact is, however, that when a direct current is used as 
stated, some current continues to flow from the aluminum to 
the lead, "seeping" through the hydroxide layer (so to speak). 

When alternating current is used instead (with a single valve) 
the latter may be said to open and close successively for each 
cycle so that one-half of each alternating current wave is checked, 
the other half passing through and having a pulsating direct 
effect. The valve, however, is not perfect in its action, and may 
be said to "leak." 

EXPERIMENT NO. 18 

TESTING A NODON VALVE WITH A DIRECT- 
CURRENT SERVICE LINE 

When one of these valves was connected with a source of 
direct current (110 volts) in series with a lamp bank and an 
ammeter, the following results were obtained at the instant the 
circuit was closed. Plus (+) to lead pole, 1.95 amperes. Plus 
(+) to aluminum pole, 1.10 amperes. 

When the circuit had remained closed for thirty seconds with 
+ to aluminum, the current was reduced to 0.15 ampere, and at 
the end of two minutes the total current flowing as indicated 
by a direct- current milliammeter was 0.020 ampere. 



AN ELECTROLYTIC CURRENT RECTIFIER 



57 



EXPERIMENT NO. 19 

TESTING A NODON VALVE WITH ALTERNATING 

CURRENT 

When alternating current is used in connection with a Nodon 
Valve, it is assumed as already explained, that pulsating direct 
current is obtained, since current is not supposed to flow from 
the aluminum to the lead. 

While this is not strictly the case, there is enough interference 
to produce a current which is sufficiently direct to be measurable 
by means of a direct- current movable- coil permanent-magnet 
ammeter or voltmeter. 

But such an instrument will respond only to the direct cur- 
rent pulsations, and since a Nodon Valve will by no means rectify 




Fig. 20. — Testing a Nodon Valve with Alternating Current. 

Instruments required are a Model 280 Weston Ammeter, range 5 
amperes, and a Weston Model 155 A. C. Ammeter, range 5 amperes. 

the current entirely, the results obtained when the so-called 
direct current is tested with accurate instruments will seem 
perplexing and apparently paradoxical. 

For instance, when both an alternating- and a direct- current 
ammeter were connected in series with a Nodon Valve, a lamp 
bank and a source of 110-volt alternating current (see Fig. 20), 
the following results were obtained: 



A. C. Line, 


Time in Minutes 


110 Volts. 





l 


2 


3 


4 


5 


10 


D. C. Instr 

A. C. Instr 


0.05 
1.80 


0.50 
1.30 


0.61 
1.25 


0.65 
1.23 


0.67 
1.23 


0.67 
1.24 


. 69 ampere 

1 . 25 amperes 



58 



EXPERIMENTAL ELECTRICAL TESTING 



EXPERIMENT NO. 20 
EFFICIENCY TEST OF A NODON VALVE 

In order to further investigate this matter, instruments 
were added to the circuit until the general arrangement was as 
shown on Fig. 21. The apparatus consisted of a Weston Standard 
meter connected with the a.c. line, directly indicating the 
power consumed. The instruments used for measuring the 
direct current were one Model 280 Voltmeter and one Model 

- : a. ; _ >. L 




D.C.VOLTMETER 




d.cammeter a.c.ammeter 

Fig. 21. — Efficiency Test of a Nodon Valve. 

280 Ammeter, which indicate with direct current only; one 
Model 155 Voltmeter and one Model 155 Ammeter. The Model 
155 instruments are of the "movable-iron" type and are operative 
with either direct or alternating current. Following are the 
results obtained: 

WATTS ON A.C. LINE=150.0 



LineVoltage.llO A.C. 


Volts. 


Amp. 


Watts. 


T>irprt c"TTPnt instruments 


36.5 
64.0 


0.9 
1.65 


32.8 + 


Alternating current instruments 


105.6 



AN ELECTROLYTIC CURRENT RECTIFIER 



59 



EXPERIMENT NO. 21 

EFFICIENCY TEST WITH TWO NODON VALVES 

IN SERIES 

Two valves were then employed in series (lead to aluminum^ 
but there was no important difference in efficiency, as shown by 
the following data: 

WATTS ON A.C. LINE=138 





Volts. 


Amp. 


Watts. 


Direct current instruments 


27.5 
46.5 


0.94 
1.55 


28.85 


Alternating current instruments 


72.07 



EXPERIMENT NO. 22 

PUNCTURING THE INSULATING WALL OF A 
NODON VALVE 

We have already found by Experiment No. 20 that a direct- 
current and an alternating-current ammeter connected in series 
with each other and operated through a Nodon valve will not 
give corresponding indications. The reason for this is fully 
explained in due course. 

But meanwhile, an interesting little experiment (original, 
we believe) may be easily performed, which consists in "punch- 
ing a hole in the insulating wall." All that is required for this 
operation is an alternating- current outfit as shown on Fig. 20 
and a piece of stiff iron wire, one end of which is bent at right 
angles to form a hook about 2 inches long. The end of this hook 
should have a sharp point. 

If the aluminum plate is touched below the surface of the 
liquid with this iron point, the direct- current ammeter instantly 
drops to nearly zero, and the total current increases, as indicated 
by the alternating- current ammeter and the improved luminosity 
of the lamp. See Fig. 22. 

If about eight lamps (16 c.p.) are connected in multiple 
for a load instead of only one, so that the current will be about 



60 



EXPERIMENTAL ELECTRICAL TESTING 



three amperes, the point of the hook will adhere to the aluminum 
to some extent, as if it were fused in by the action of the current. 

Bubbles rise freely from the hook while in contact with the 
aluminum, indicating that the aluminum hydroxide will not 
adhere to the iron; and hence, since the point of the hook has been 
forced through the layer, it conducts current from the aluminum 
through the liquid to the lead, changing the apparatus into a 
simple liquid resistor. 

Only one valve should be used to get the best effect in this test. 



Construction and Arrangement of the Electrolytic Current 

Rectifier 

It is obvious that the only effect produced by one or more 
Xodon valves in series, is to impede the flow of an alternating 

current in one direction. The 
resultant direct current cannot 
have an efficiency greater than 
50 per cent of the total alter- 
nating current, and is actually 
only about 25 per cent or less. 
It is possible,, however, to obtain 
greater efficiency by arranging 
four valves in the form of a 
parallelogram and connecting the 
alternating current in such a 
manner that both halves of the 
current will be utilized to pro- 
duce a direct current. 

One of these rectifiers was 
purchased for experimental pur- 
poses and tested in the Weston 
laboratories. It consisted of four porcelain jars, each about 
5% inches in diameter and 11 inches in height.. provided with 
an insulated top and binding posts. 

Each jar contained a rod of aluminum and two plates of lead, 
the latter being connected together. The solution used was 
bicarbonate of soda. The general design was such that a large 
percentage of the alternating current was converted into direct 
current. 




Fig. 22. — Puncturing the Insu- 
lating Wall of a Xodox Valve. 



AN ELECTROLYTIC CURRENT RECTIFIER 



61 



The Theoretical Operation of the Electrolytic Current 

Rectifiers 



The current from an a.c. source enters at a, see Fig. 23, 
is checked at k, but may flow through the lead plate b to c to d, 
is again checked at i, but may flow through the instrument (or 
load) to e, continue through / and g and out to h, constituting 
half a cycle. The other half operates through h, is checked at 




Fig. 23. — The Electrolytic Current Rectifier. 

g, but follows ; and i to d, is checked at c and flows through 
the instrument to e, etc. 

A rather surprising feature of these rectifiers is that the 
direct- current voltage of the apparatus when the voltmeter 
is connected as shown on Fig. 23 is sometimes 20 per cent higher 
than the a.c. line voltage. This is only the case, however, 
when the direct current used is negligibly small. 



62 



EXPERIMENTAL ELECTRICAL TESTING 



EXPERIMENT NO. 23 

EFFICIENCY TESTS OF A COMMERCIAL ELECTRO- 
LYTIC CURRENT RECTIFIER 

In order to obtain some data in relation to efficiency, a test 
was made having a continuous run of two hours. See Fig. 24. 
Following are the results obtained: 





A.C. LIXE, 


VOLTAGE=110 






Watts on 




Pulsating Direct Current. 


Tern, of 
Solution 


Efficiency 


A. C. Line 


Volts. 


Amp. 


Watts. 


Time. 




320 
380 
450 


85.0 
87.0 
85.0 


1.70 
1.72 

1.70 


144.5 
149.6 
144.5 



lhr. 

2hrs. 


23° C. 
32° C. 
42° C. 


45.1% 
39.4% 
32.1% 




TO A.C.LINE 

Fig. 24. — Efficiency Test of ax Electrolytic Current Rectifier. 

When the apparatus was connected directly with the a.c. 
line and no direct current was drawn, 45 watts were consumed. 
When nothing but a high resistance voltmeter was connected 
with the direct- current binding posts, it indicated 133 volts. 

Alternating- current voltmeters and ammeters were also 
used in making this test. Their indications taken simultaneously 



AN ELECTROLYTIC CURRENT RECTIFIER 



63 



with the direct current observations averaged 11 per cent higher. 

Some experimenters state they have obtained greater effi- 
ciency by introducing a transformer in the circuit so as to reduce 
the voltage to 55 or below. 

Following is the result of a test made under such condi- 
tions : 

A.C. VOLTAGE=55 



Watts on 


Pulsating Direct Current. 


Tem. of. 
Solution 


Efficiency 


A. C. Line 


Volts. 


Amp. 


Watts. 


Hours. 




88.0 
80.0 

76.0 


25.1 
22.0 
20.1 


1.27 
1.10 
1.05 


31.88 
24.20 
21.10 




1 

2 


25. 2C. 
28. 0C. 
30. 0C. 


36.2% 
30.2% 

27.7% 



Note. — It should be distinctly understood that it is not 
claimed that either of the results obtained is conclusive. On 
the contrary, it is quite probable that increased efficiency may be 
obtained. It is also likely that some modifications of the 
apparatus including a water jacket or some other contrivance 
for keeping the temperature from rising unduly would have 
advantages. 

Caution. It is safest to include a lamp bank or some other 
resistor in the line when the rectifier is first used or after it has 
been idle for even a short time. There is often a current surge 
of 20 or more amperes when the circuit is first closed. This is 
due to the fact that the hydroxide has not had time to form. This 
surge also causes a strong pulsating current to develop at times, 
and unless fuses are put in both lines, damage may be done to 
apparatus in circuit. 

These rectifiers may be used to charge small storage batteries, 
but care should be taken to connect an ammeter in circuit to- 
gether with a rheostat or bank of lamps, in order to regulate 
the current. 

The top part of the jars as well as the cover to which the 
elements are fastened should be dipped in hot paraffin before 
setting up, so as to prevent the solution from creeping. 

The liquid should occasionally be renewed, since it seems to 
deteriorate. 



64 EXPERIMENTAL ELECTRICAL TESTING 

Instrument Indications in Connection with a Rectifier 

The reason for the difference between the indications of the 
direct- and alternating- current Weston instruments when used 
to measure the output of an electrolytic rectifier, is explained 
in an article by Albert Nodon, in Vol. I, of the Transactions of 
the International Electrical Congress, St. Louis, 1904, entitled 
''Electrolytic Rectifiers — An Experimental Research," page 510. 

This experimental research includes charts showing the wave 
form of the rectified current as obtained by means of the ondo- 
graph or oscillograph. 

If this rectified current is measured by a Weston alternating- 
current ammeter, the result is that the instrument readings repre- 
sent the effective current, which will be the square root of the 
mean square of the instantaneous values. 

Whereas, if a direct- current ammeter is used, its indications 
depend upon the arithmetic mean value of the instantaneous 
values of the pulsating current. If the transformation were 
perfect the difference between the indication of the two types 
of instruments would be 11 per cent. 

The fact is, however, that the transformation is not perfect. 
The results obtained with a single valve prove this, and even 
when four valves are arranged in parallelogram form, there is 
a loss due to leakage as well as to resistance. This can be 
directly proven by measuring the pulsating current by means of 
an induction meter which will not indicate with direct current. 
It can be simultaneously shown that the direct -current instru- 
ment responds only to the direct- current pulsations ; the alternat- 
ing-current instrument gives the combined effect of direct and 
alternating current; and the induction meter indicates only the 
alternating current (or leakage), its indications being approxi- 
mately the difference between the other indications. 

In charging storage cells and in running direct-current motors 
as well as in the electro-deposition of metals, the above state- 
ments should be taken into consideration, since it is obvious 
that the only effective current for such work obtained from 
rectifiers of this type will be due to the direct-current pulsations. 
An article entitled "The Chemistry of the Electrolytic Current 
Rectifier," by Donald McNicol, will be found in the August, 
1913, number of the "Electrician and Mechanic." 



WESTON DIRECT-CURRENT MOVABLE-COIL SYSTEM 65 



THE WESTON DIRECT-CURRENT MOVABLE-COIL 

SYSTEM 

(Prepared by the Compiler) 

This system consists primarily of a coil which can rotate 
freely in a strong magnetic field produced by means of a per- 
manent magnet. When a current is flowing through it, this 
coil acquires magnetic properties and tends to assume a position 
which will reduce the distance between its poles and the oppo- 
sitely magnetized poles of the permanent magnet. Springs which 
also serve as current conductors tend to oppose the movement 
of the coil* 

The Milliammeter 

An instrument which consists only of a coil, a magnet, a core 
and an elastic metallic conductor for controlling the movement 
of the coil, in short a "system" as described above is in its 
simplest form a milliammeter. All Weston direct- current mov- 
able-coil systems are fundamentally uncalibrated milliammeters, 
although they may differ in size, in the strength of their magnetic 
fields, in the number of turns of wire in their movable coils, and 
in mechanical details. This is the case because all systems of 
this type are operated by means of a small current; and the 
extent of the deflection produced depends upon the strength 
of this current. 

The Millivoltmeter 

The system as described, is also an uncalibrated potential 
indicator or millivoltmeter, because a definite electromotive 
force is needed to overcome the resistance of the movable coil 
and force a current through it. If, therefore, we consider the 
system in its simplest form as consisting only of a movable coil, 
a core, a magnet, and a pair of springs directly connected to a 

*See also Monograph B-2. 



o: z:i?i7 i t i :::;:::; .-.i 77-777 



\ir of tending posts by means of leads of negfigihlft 
then it follows that, for axy defection of the movable coH at a 

-z-i-i ::-::-:: ~: :■: : --:-.: .... :'::z\: :: :'--: :z-.-: -;■- :'zz: i- 
--::: :-. Azi zz:3 ±f rrsir..iz:s= :: ±r n:"3,:lr : :z 3Z3 5zr.zr5 
— 7 il—3,75 Z3 ;:t 53ZZ3 s: 3 zzzi vz:^:::— t 7 ilz :77:~5 ±3.: 
::: z:-en :■.-_- iiz±zzs ".he :^:z:r>f ::::r :z:zzz3z :■: 

-It :tSZ5Z.3ZZ 33: II '1: — I v 3 3 '.3 Mil 3Z3 3.ZL 1 IZZZZZ 
3333333 ZZTTtZZ Z_ 3.~3~5 :*r ZZr 533Z3 ZZZ-fSS 53XZZ3, Z3S3~.- 

: ii i-:-i :.: :ie :-■:--. 

Z'zt M:T=ble-C::I C:~;:=;i: 



::' zztttZz: ii: 

e Z3 : z^r..izzzizz.z z: 3 zzrzzz-zz =7 ren ±3,: :.= z: 53" 3 57-5-cZZ 
::' 3 :3z:3 3z 7~z~ :: : . 3 e 5 3331 iiier 3 7 z:rzz:7 ::zzz::z5 
n:7 :: 33 5-333-= 3:3 is-rc 313 vz:7zir:zTs:le 7:: z1.5-.3z33 ::' 
zzzz-n: :3zz:z33 :.: 7::.iiz 3 7.7 5.:^ :3Z3-:z:z :.5 II 3Z33-7- 
3Z3 " -3 7 : 3 ; : c ' 3 z : 3 ; : - 3 3 Z3 : ' 3 z: 3z : : 5 : : zzz 5 : z -. z : 3 3 3 zz : 

": ' ZZr, ~Z 1 Z 3 =. " 3Z ZZ.'.i LZ35Z 3Z I r I»rZZZ 



3Z 3 Z: 33 33 Z3-Z33Z3Z Z !!OZ 



"." 7. — e:er 



7: 3~3Z. 3Z3 rzzzr :: sz:z 3z z ; :rzzz: ::: -zz::: Z1335- 
mementSy it will be necessaiy to add a resistor to the enrmt 7 

::' 53 z_ 3 Z3 ; z: zz :zzz5 Z3r :z :.= 7zzzi 
E 



: 3 '.-:.-. :;z;3 :ze 3333Z 
1 



.zz'5z:z" "..: i_: 
3 zz: :---3z:3 : 

~ . . 3 3 ~ 3 : 



WESTON DIRECT-CURRENT MOVABLE-COIL SYSTEM 67 



The Ammeter* 

In attempting to use the movement already referred to for 
current measurements, it will be apparent immediately that 
no current greater than .010 ampere should be passed through it. 
If therefore a larger current than this is to be measured, some 
contrivance must be attached which will permit a larger current 
to flow, and yet limit the quantity flowing through the move- 
ment. This is most easily accomplished by means of a divided 
or shunted circuit. 

For instance, if a resistor is constructed of insulated wire 
having the same resistance as the movement, and is connected 
directly with the binding posts of the instrument, and the 
binding posts are then connected with a source of current, it may 
be deduced that such a current will split; and since the resistor 
has the same resistance as the movable coil, the current will 
split evenly, half of it going through the movement and half 
through the resistor. But, the movement will only respond to 
the current flowing through it, and not to the current flowing 
through the resistor. Since these currents are alike, it follows 
that the pointer will indicate half of the total current flowing. 
In other words, the ampere range of the instrument has been 
doubled. 

To determine how to still further extend the ampere range 
of the instrument it is only necessary to refer to the laws relat- 
ing to divided circuits. The current flowing through two parts 
of a divided circuit will be directly proportional to the resist- 
ances of these circuits. If, for instance, the shunt coil measured 
.06 ohm and the movement 6 ohms, then the current would 
be as .06 is to 6, that is, the current through the shunt would be 
100 times as great as that passing through the movement. For 
it must not be forgotten that the voltage at the binding posts 
is the same for the movement as it is for the shunt coil, and that 



*For data relating to Weston movable systems, see also "Elements of 
Electricity," Timbie, Chap. XIV; "Physics," Mann and Twiss, page 169; 
"Practical Physics," Black and Davis, page 284; "Laboratory Manual," 
Black and Davis, page 64; "High School Physics," Carhart and Chute, 
page 371; "A High School Course in Physics," Gorton, page 405; "Elec- 
trical Instruments and Testing," Schneider and Hargrave, Chap. 4 and 
"Lessons in Practical Electricity," Swoope, Lesson 18. 



68 EXPERIMENTAL ELECTRICAL TESTING 

consequently the less the resistance of the shun- U r will 

be the current flowing through it. A point could therefore be 
reached where the shunt would have so low a resistance that it- 
would earn* practically all of the current, and not enough would 
flow through the movement to make it operative. Such a shunt 
would be described in practice as not having enough "drop.'' 
meaning that the potential difference between its extremes would 
be insufficient for the purpose for which it was intended 

In practical work the shunts are usually constructed to have 
a standard drop of 50 or 100 nullivol:. Thf resistance : the 
system is increased by adding non-inductive zero temperature 
coefficient material in series, so as to increase the e.m.f. required 
to produce a full scale deflection to 50 or 100 millivolte or some 
other value, according to the type of instrumri;- and (he drop 
of the shunt. 

THE WESTON ALTERNATING- AND DIRECT- 
CURRENT "MOVABLE IRON" SYSTEM 

1 : r pared by the Compiler) 

The direct- current movable-coil system described in the pre- 
ceding article is inoperative with alternating current, be 
its field as produced by a permanent magnet has fixed pol; 
Consequently when an alternating current is ;::-:: through 
the movement, the polarity of the movable coil is con- 

tinually reversed, and the movement oscillates instead of being 
deflected. The effect of an alternating current when applied to 
a direct- current movement can be plainly seen by the vibra- 
tion of the pointer,* but of course there is no continuous motion 
in one direction by means of which an alternating current could 
be measured. 

The movable element of the Weston movable- iron system con- 

'A a small curved piece of iron fastened I 

shaft. This shaft is also provided with a truss form of pointer 

made of thin aluminum tubing, to which is attached a balance 

cross and a small vane. The shaft moves in jeweled bearings. 



*Experiments of this kind if protracted, neither improve the sharpness 
of the pivots nor lengthen the life of the pointer of a d.c. instrument. 




Fig. 25 .—Phantom View of Weston Models 151, 155, 156, 159, 160. 
Moving Parts of "Movable-Iron" Voltmeters. 




Fig. 



26. — Phantom View of Weston Models 151, 155, 156, 
Moving Parts of "Movable-Iron" Ammeters. 



159, 160. 



THE WESTON "MOVABLE-IRON" SYSTEM 69 

Near this movable element and concentric with it is a small 
curved tongue of soft iron which is rigidly held by a suitable 
support. (See Figs. 25 and 26.) 

Surrounding these is a field coil, made up either of a large 
number of turns of insulated wire when the instrument is to be 
used for the measurement of e.m.f. or else of one or more turns 
of heavy conducting material, when designed for the measurement 
of current. 

Principle of Operation. When a direct current is passed 
through the field, the movable element and the fixed tongue 
of iron become magnetized by induction ; but since they are 
within the field coil, their juxtaposed ends will have like polar- 
ities. Consequently these poles will repel each other. The 
only resultant motion possible is the rotation of the movable 
element. 

When alternating current is used, the polarity of the field 
coil will be alternately North and South, the number of reversals 
depending upon the frequency. 

The polarities of the movable and fixed iron parts of the 
system will also reverse correspondingly, but although the jux- 
taposed parts will have constantly reversing polarities, they will 
have like polarities in relation to each other, and therefore will 
necessarily repel each other continuously, thereby imparting a 
rapid series of impulses to the movable element, causing a deflec- 
tion in one direction only. 

This deflection is opposed and therefore controlled by the 
action of a delicate spiral spring; hence the extent of the rota- 
tion depends upon the strength of the current flowing through 
the field coil. 

The peculiar shapes as well as the relative positions of the 
iron parts are features which are the outcome of much the- 
oretical work and numerous experiments. As a result, the instru- 
ment is almost entirely free from hysteresis or lag; that is to 
say, the magnetization, demagnetization, and remagnetization 
of the iron, will be practically perfect. 

If the instrument is designed for current measurements, it 
is so arranged that all of the current passes through the field 
coil. This is also the case when intended for the measurement 
of e.m.f., but an adjusted resistor lies in series with the field coil. 



70 EXPERIMENTAL ELECTRICAL TESTING 

The resistance of the instrument is thereby increased, and the 
quantity of current which may flow is regulated. Precisely as 
in direct- current movable-coil instruments, the amount of cur- 
rent which will flow, depends upon the e.m.f. of the circuit across 
which the instrument is connected. 

The vane or damper moves in a fan-shaped pocket which is 
shown in Fig. 26 with the cover removed. When this vane is 
enclosed it damps the movement of the system without mechani- 
cal friction. That is to say, the vane does not touch any part of 
the receptacle but moves through confined air. 

The scales of these instruments are open and fairly uniform 
throughout four-fifths of the total range of deflection.* 

CO-OPERATORS 

We extend our hearty thanks to all physics instructors who 
have assisted in the preparation of this monograph, either by 
their encouraging approval of our previous efforts, or by their 
suggestions and direct contributions. 

Among many others, we are especially indebted to the science 
teachers whose names we append, with occasional extracts from 
their communications: 

Ames, C. G., Instructor in Physics, High School, Berkeley, 

Cal. 

"I would be glad if you can spare me two extra copies of monograph 
B-2 for class use." 

Andrews, A. P., Instructor, Department of Physics, Min- 
neapolis. Minn. 

''There can be no possible question as to the service you are rendering 
schools. Personally, I expect to profit by it." 

Baer. C. E.. Department of Science, The Lincoln High School, 
Seattle, Washington. 

''Please send all Monographs or other literature descriptive of such of 
your instruments as may practically be used in our modern high schools. 

I am on a committee of Seattle Physics teachers, appointed to outline a 
revised course in electricity from beginning to end, and need your co-opera- 
tion." 



*See Monograph B-o for additional information relating to these 
instruments. 



CO-OPERATORS 71 

Barber, Fred D., Illinois State Normal University, Normal, 
111. 

Barrett, J. T., Department of Physics, Lawrenceville School, 
Lawrenceville, N. J. 

"Personally I was glad to see you entering a field where Tin Students' 
Instruments had been the only low-priced supplies available." 

Beals, Frederick H. Department of Physics, Barringer 
High School, Newark, N. J. Formerly Prof, of Physics, Occi- 
dental College, Los Angeles, Cal. (Deceased.) 

"I hope you will continue the good work of issuing monographs con- 
taining experiments of practical value, experiments from the commercial 
testing laboratories and from workshops, exercises more nearly touching 
daily experience and commercial life than have hitherto been customary in 
school; real problems of the work-a-day, experiments which have living 
reality in the school laboratory." 

Black, Prof. N. Henry, A.M., Science Master, Roxbury 
Latin School, Boston, Mass. 

"I have yours of the 20th inst., and am much interested in your efforts 
to give the schools a really good electrical measuring instrument, and at the 
same time to suggest how they may be used to get nearer to the real 
practical electrical problems. You may be interested to know that last 
year when I was getting out the Laboratory Manual to go with the text- 
book, your voltmeter and ammeter was the only form of electrical direct- 
reading instrument, which I felt enough confidence in to illustrate. (See 
Fig. 38 of Lab. Man.). Go ahead with this good work." 

Boynton, W. P., Professor of Physics, University of Oregon, 
Eugene, Oregon. 

"Your monographs are of interest to me personally, and also of value, 
as I am called on to advise present and prospective teachers in physics in 
the High Schools of this State." 

Btjrgin, Bryan 0., Department of Science, Albany High 
School, Albany, N. Y. 

Burns, Elmer E., Instructor in Physics, Joseph Medill High 
School, Chicago, 111. 

"I have read the monograph carefully and do not see any way in 
which it could be improved." 

Cady, W. G., Professor in Physics, Wesley an University, 
Middletown, Conn. 

"The idea of issuing these monographs is a good one." 



EXPERIMENTAL ELE1 777 1 AI 77-7 



:■-. . " > £ : :::-/::'::: ::' ± 7: * .:-:7 * 






_: _ ■;.. 

Z m ._;: :i. rrir::: ::' !.-__-„ Z.t: : . T ■ _j _ . -; 

take this opportunity to congratulate you upon file wade which you lure 
done in bringing practical problems of imlin*4ind fife dire c tly to the school. 
If industrial plants in general would take this same attkndp, it would 

■it 5:-h:«:l= a mihcnrr ~ i_ :hr" ■ :.. 

-To -what extent and m what way could I secure more copies of this 
monograph? 

Out::: >i: Precipe: :: Piys::-=. Hirm OcZigc Hit in 
Ohio. 



"I appreciate the monographs which tout company is send in p out 
and can make use of fo"»p ib***ff* in them in the laboratory work of my 

studente." 

Dowd, Me. J. E : cal High School, Worcestt: 



"I will state that your monograph proved of great service and value 
to me, as much of the electrical apparatus we have is of your make, and 
the topics dwelt upon offered much information about them." 

Deapee, Jason T.. Ms c :c: in Science, High School, Holyoke, 

• I plan to equip my laboratory at once with whatever is needed to 
carry out all that is outlined in your Monographs in rlawiilany Testing.* 



Eastman I .-.?-_ ^ience Department, High School, Atlantic 

City. N. J. 

"I find your monograph B-2 very helpfuL" 

I sxbt. Albeit Zistem TTigft School, Bay City. Mich. 



"Your monographs have proven a help to me. I have adopted several 
of the 4"» pn iinwifa you Awn Jm*. in my laboratory cum he. 

Z:~ .-_:-: • :?:'.""=: - I -\ ::.-..' I . :i ":- 

lege, Parkville. Mo. 

: very glad to receive foe monographs B-l, B-2 and B-37 



EX. H. ( I 

Sac: . 

V: • - :. - -:..-....--. 

11. .1 -~.i\-.LZ rip-fr-HrLl: 

Evans. Wm 7 7- - bool, Brooklyn ,N Y 

7: Head o: Science DepartmeL Everett Higfc 



CO-OPERATORS 73 

Fischer, H. F., Professor University of California, Berkeley, 
Cal. 

Foerste, August F., Instructor in Physics, Steele High School, 
Dayton, Ohio. 

Flanders, M. M., Bliss Electrical School, Takoma Park, 
Washington, D. C. 

"I would like any technical data you will furnish in regard to principle 
of operation of your soft-iron instruments." 

Fox, John E., Western State Normal School, Kalamazoo, 

Mich. 

"I think your plan an excellent one and shall be glad to suggest some 
materials for future monographs which will be of interest to physics 
teachers." 

Gardiner, F., Headmaster of the Yeates School, Lancaster, 
Pa. 

"I should like to see experiments in efficiency tests, on the small 
transformer, electric cooking utensils and current capacity test on com- 
mercial fuses." 

Glenn, Earl R., Carter H. Harrison Technical High School, 
Chicago, 111. 

"I have read the literature you sent with great interest and profit. 
Science instructors owe much to the company you represent." 

Gorton, F. R., Professor of Physics, Michigan State Normal 
College, Ypsilanti, Mich. 

"Your communication regarding the publication of B-4 compilation 
of laboratory exercises is at hand. I think the subject matter excellent, 
but feel that the experimental part is too full in some points and deficient 
in others. I shall be glad to see the publication." 

- 

Graham, Prof. W. P., College of Applied Science, Syracuse 

University, Syracuse, N. Y. 

Griffin, Chas. E., Head of Science Department, San Ber- 
nardino High School, San Bernardino, Cal. 

"I think at the present time the greatest need in the teaching of elec- 
tricity in our high schools is an apparatus for the demonstration of alter- 
nating-current phenomena. Your plan of co-operation appeals to me as 
being especially desirable." 



74 EXPERIMENTAL ELECTRICAL TESTIS 

Hammond. H. EL, Physics Department. Kalamazoo Public 
Schools. Kalamazoo, Mich. 

"I believe your company is doing a good work in putting out these 
monographs, and I think that there ought to be a response in a business 
:: WesA :n instruments do what they are intended to do." 

Hathaway. F. R.. Physics Director, Classical High School, 
Salem. Mass. 

"I received the two monographs and hope to take advantage of the 

suggestions contained therein, in teaching electricity this coming winter." 

Hedeice, Wm. A.. Instructor in Physics. McKinley Manual 
Training School, Washington. D. C. 

T like the monographs very much and their aid has persuaded one of 
the teachers 1 : 1iy the drop of potential along a wire, that I was not able 
to do before. We will take great pleasure in calling the attention of the 
physics Teachers' Ass'n to your instructive monographs." 

Hull. Pbof. G. E.. Wilder Laboratory, Dartmouth College, 
Hanover. X. H. 

•You are doing a great service to scientific teachers in sending out this 

literature." 

Ixgvalsox. Edwaed. Instructor in Physics, Lanesboro Public 
Schools, Lanesboro, Minn. 

"There is certainly need of reform as far as Lab. measuring apparatus 
is concerned, and I believe you are doing much good in circulating such 
literature as your monographs. The toy apparatus ice have is a farce. Most 
science teachers know this but are handicapped in improving conditions." 

Kelebeb. C. M.. Department of Physics and Chemistry, 

-burgh High School, Petersburgh, 111. 

"Perhaps 5::_e science teachers would find it suggestive if you were to 
describe a method for making efficiency ----- of commercial electric heating 
units such as disk stove, percolator, etc. I have found such exercises very 

conducive to interest in my class work." 

Killex. A. H.. Instructor in Physics, Flushing High School, 
Flushing. N. Y. 

Lyon, Leslie W.. Department of Physical Science, Burling- 
ton High School, Burlington. Iowa. 

• I would particularly like to have discussed the measurement of electric 
I in such experiments as determining the efficiency of electric lights, 
electric iron, heating ph- 



CO-OPERATORS 75 

Marble, Milton M., Department of Physics, New Haven 
High School, New Haven, Conn. 

''Please send with instruments, 25 copies of Monograph B-2 for students' 
use, and oblige." 

Marvell, Sumner E., New Bedford High School, New Bed- 
ford, Mass. 

"I found your monographs helpful in the physics work of the school. 
I have always felt that a closer contact between our teaching and com- 
mercial apparatus would be of great assistance to us." 

McKenzie, Monroe R., Professor of Physics, Parsons Col- 
lege, Fairfield, Iowa. 

Moore, Prof. J. C, Master in Science, Worcester Academy y 
Worcester, Mass. 

"I wish to say that the monographs, especially B-2 and B-3, are excep- 
tionally useful to science teachers. We hope that you will continue to issue 
them and suggest practical work in electrical measurement. You will doubt- 
less be interested to know that they have stimulated us to equip a labora- 
tory for electrical work, separate from our regular physics laboratory." 

Moore, J. Colin, Instructor in Electricity, Lake High Manual 
Training School, Chicago, 111. 

"I shall be glad to make some suggestions for experiments which may 
be of use to others." 

Nye, Arthur W., Department of Electrical Engineering,. 
University of Southern California, Los Angeles, Cal. 

"I received the monographs early in the summer and was favorably 
impressed with them. I hope that you will continue their publication and 
that you will also publish some dealing with high-grade electrical instru- 
ments. There seems to be a lack of printed material about really high 
grade practical engineering electrical measurements." 

Pace, Miss Lillian, Central High School, Washington, D. C~ 

"I have always thought that something of the sort sent out by makers 
of instruments which we use would be most acceptable and am glad you 
have entered in this work. It will give me pleasure to co-operate with you 
and make suggestions." 

Peet, J. C, Department of Electricity and Chemistry, Tech- 
nical High School, Harrisburg, Pa. 

"Your experiment on the Heating Effect of current is especially good. 
I should like to see you add one on Chemical Effect, using the copper volt- 



76 EXPERIMENTAL ELECTRICAL TESTING 

am m eter to standardize an ammeter. Keep up the good work started in 
these monographs." 

Phujppi, H. C. Department of Physics. State Normal School, 
Bellingham, Wash. 

"I should be glad to hare you discuss in future monographs 
practical electrical measurements suitable far high-eehool work or for the 
first two ye&rs of college physics 

Pond, Ethel C. Physics Teacher Sycamore High School, 

Sycamore, 111. 

*T consider publications such as yours the most valuable help a pL;^;: ; 
teacher can receive, and I wish to express my appreciation." 

Poore, Chas. D., The Northern Normal and Industrial School, 
Aberdeen, South Dakota. 

'I remember on getting your monographs, of at once being struck with 
the need of just such things in perfecting my electrical eoui 

Randall, J. A., Pratt Institute. Brooklyn. N. Y. 

Rat-cliff. R. P., Department of Physics and Chemistry, 

Central Normal School. Danville, Ind. 

"Monograph B-2 is very valuable to us ? especially, in that it gives 
sample experiments from the practical electrician's point of view. Tlria n 
a phase of the work we wish to develop.*' 

Reed, Harold B.. East High School, Cleveland. Ohio. 

'"'Have read the monographs with the greatest interest. They are a 
real contribution. Shall try out several of these experiments this 
Shall be glad to do anything possible to help along a good cause." 

Rial, David. Instructor in Physics, State Normal School. 
Mansfield, Pa. 

Rood, James T., Professor of Physics and Engineering, 

Lafayette College, Easton, Pa. 

"Your idea that these monographs shall have so much interns 
that they will be carefully kept in file :- is I :hink. most 

admirable. Pre s 

Rothermel, John J.. Physics Laboratory. Eastern High 

School, Washington D. C. 

4 *I hope to be able to take some work on effio: "f small b 

formers, and probably also in electric cooking utensils. I should 1 
glad to have about half a dozen copies of Monograph B-2 and B-3 
could use with one of my classes in the aU experiments 



CO-OPERATORS 77 

Smith, Ernest Reveley, Instructor in Physics, Syracuse 
High School, Syracuse, N. Y. 

Turner, Geo. M., Hasten Park High School, Buffalo, N. Y. 

"Our work with the triple-range voltmeters and double-range ammeters 
Model 280 proved very satisfactory. No instrument was abused by any 
pupil either by accident or intent. It is our purpose to extend their use 
during the course in electrical work of the present school year." 

Twining, H. L., Head of Physics and Electrical Engineering, 

Los Angeles High School, Los Angeles, Cal. 

"You are making a move in the right direction in developing instru- 
ments of accuracy for high schools. I am writing a text on elementary 
electricity covering the first year's work and also a manual to accompany 
it. In it I am going to feature your instruments and recommend their 
use. I do this because they are the best that the world has to offer." 

Twiss, G. R., Professor of Physics, Ohio State University, 

Columbus, Ohio. 

"Replying to your letter of January 21st, which has been overlooked 
because of the pressure of semester examinations, I would say that I am 
very much interested in your enterprise looking to the publication of mono- 
graphs on experiments that can be made with standard commercial instru- 
ments, and that have direct commercial and industrial bearings. I think 
that if wide publicity is given to such experiments, the movement cannot 
fail to be productive of much good to the pupils of the high schools. I 
should be glad to receive all the pamphlets of this character that you have 
issued up to date, and to be placed on your mailing list for other material 
of similar interest that you may issue from time to time." 

Vawter, C. E., Professor of Physics, Virginia Polytechnic 

Institute, Blacksburgh, Va. 

"I have four of your miniature instruments and I consider them the 
greatest find that I have made for my electrical work in a long time. I 
shall get more." 

Wauchope, Prof. J. A., Department of Physics, Mechanics 

Arts High School, St. Paul, Minn. 

"I sincerely hope you will continue the publication of the mono- 
graphs, as the suggestions are helpful to me and I am sure must be to many 
other teachers. This is excellent work that you are doing." 

Webster, Evans, Head of Physics Department, English High 

School, City of Lynn, Mass. 

"What we need most in our elementary laboratories is a galvanometer 
in portable form for use with the slide wire bridge, and which can be used 
without a shunt box, costing not over six or seven dollars. The galvanom- 
eters usually found (made by ... ) are the most exasperating pieces of 
apparatus to put in the hands of students that I know of." 



75 IX?Z7.::/ZXTAl ILZCTBICAl TESTEN 

Wood. Lt^t>- H.. Professor Department of Physical Science, 

Vi::i ri-lr^r L':.-rZr ? I lH". Vlr" . >~rb. 



tt ¥e hare received your monographs B-l 7 B-2 and B-3. We appreciate 
them toy modi. For a long time the work in electricity in our science 
department has been, altogether too theoretical, and we welcome any 
T^r^pr" that will tend to make the work more practical. We are adopting 

WruEy R. M-, Professor of Physes, Marshall College, Hunt- 
W.Va. 



"Most high schools buy their equipment as yon know, to fit their 
particular comae. K the laboratory manna Is which are put out by the 
book companira to accompany audi testa aa Miffiken & Gale, Carhart <x 
Chute, Gorton, or Hoardiey s new book, only ffontainpd cuts of your minia- 
ture instruments and nrccam directions for then* use in the experiments 
in rlrC~:~-:;~ y.'i ~ :_ i ~~ -' t.?~~ kjlmIs ~~r~—z y:urs mi •mi.z :lr~ 



AN APPEAL 



If our monographs are of service to the reader 
we have succeeded in bringing him in touch with the 
earnest efforts of others, then, from a utilitarian stand- 
point, it would seem that the most suitable return 
instructor :an make, will be to recipro- 
cate with new material or helpful suggestions, through 
the medium of our publications. 



LIBRARY OF CONGRESS 



005 915 058 3 • 



